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Vol. 19, No. 3, May 25, 2004 In this
Issue |
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2004 Trevor Nichols Research Complex Trapline Data -
Apple scouting through the summer months |
The summer period covers over three months of the growing season and in some cases several generations of a single pest. We will introduce pests, and the appropriate scouting techniques, in the chronological order that they will most likely first appear the orchard, including: European and twospotted spider mites, green apple aphids, spotted tentiform leafminer, tarnished plant bug, apple scab, plum curculio, and white apple and potato leafhoppers. European red mite and twospotted spider mite scouting continues through the season, although thresholds may change. We will monitor mites using a 100-leaf sample, 50 percent spur leaves and 50 percent shoot leaves, throughout the summer period. Control measures may be warranted for mature, healthy trees based on the following thresholds: § Two to three mites per leaf from petal fall to mid-June § Five to seven mites per leaf from mid-June through July § Ten to 15 mites per leaf in August. The presence of predaceous mites (greater than one per leaf) may justify delaying a treatment and repeating the cycle the following week. Monitoring for green apple aphids (GAA) will continue as long as new terminal growth is present. GAA prefer to feed on the underside of leaves on growing shoot tips and stems. Estimate the average number of aphid infested leaves on terminals. Generally, an average of three to four infested leaves is needed before fruit damage from honeydew occurs. In young orchards, lower levels of aphid infestation (one to two leaf colonies) will inhibit growth of trees. Continue to monitor egg and larval stages of spotted tentiform leafminer, but now include the tissue feeding stage. Use the accompanying table for monitoring and treatment decisions. Spotted tentiform leafminer
Continue to monitor for tarnished plant bug, mindful that orchard mowing or droughty conditions may drive adults from the ground cover into the trees. Also continue to monitor for new apple scab lesions on fruit and leaves, new symptoms of powdery mildew, and fire blight infections. Monitoring for plum curculio adults and egg-laying should continue for at least six weeks after petal fall. Any new fruit damage should be noted as to location and severity. Oriental fruit moth (OFM) monitoring will continue with traps, but the focus for damage assessments should now be on fruit. Fruit injury from OFM is often indistinguishable from codling moth injury. Control treatments for first generation OFM egg hatch occur at 150 to 170 degree days post biofix GDD45, second generation egg hatch at 1125 to 1150 GDD45, and third generation at 2250 to 2280 GDD45. Within two weeks of petal fall, you may begin to see white apple leafhopper nymphs and potato leafhoppers. White apple leafhoppers are the more significant of the two and will appear as pale white nymphs on the lower surfaces of older leaves. These nymphs will develop into adults over a 30-day period, the second generation emerging 30 days later. Note the difference between the white apple leafhopper and the potato leafhopper, which is green and stays mostly near the actively growing terminal leaves. We will monitor for first generation white apple leafhopper by counting the number of nymphs found on 100 leaves selected from leaf clusters and reporting this as the average number of nymphs per leaf. For the second generation, we will select our 100 leaves from the mid-shoot area. Thresholds for trees with sparse canopy and a heavy crop load is less than for trees with luxurious canopies. Generally, one to three leafhoppers per leaf will bleach around the midrib only, eight per leaf will stipple the entire leaf and create problems for workers at harvest. Obliquebanded leafroller pheromone baited traps should be placed in the orchard three weeks after petal fall, and monitored for the first sustained catch for biofix purposes. The OBLR model will predict egg hatch and help determine when to start monitoring for larvae. Larva from the first, or summer generation, may be found in a couple of different locations in the tree. Newly hatched larva frequently head for the tip of the new terminal growth where they will feed on unfolding leaves. Larva may also feed on fruit, especially where it is clustered, by attaching a leaf to the fruit and feeding underneath it. These larva are more difficult to detect but are important due to their potential of causing significant economic loss. Monitoring will consist of counting the number of larva found on 100 terminals and fruit clusters. Obliquebanded leafroller
San Jose scale should be monitored with pheromone baited traps if there is a history of pest problems. Yellowish crawlers generally are present 300 to 350 GDD50 after the first catch of either generation. Note the presence or absence of crawlers and their subsequent damage to fruit. Dogwood borer overwinters as larvae in the burr knots or trunk of the tree. You should be scouting for reddish-brown frass and pupal skins in and around bur knots as an indication of an infestation. Codling moth monitoring will continue with traps, but with the addition of damage assessments on fruit. Note the location and severity of any fruit injury. Codling moth
Approximately six weeks after petal fall or before 900 GDD50 (late June in southern Michigan to second week of July in Northwest Michigan), apple maggot sticky traps should be placed in the orchard. Adult fly emergence often follows rainfall events with emergence typically delayed if the soils remain dry. Peak emergence generally occurs between 1400 and 1700 GDD50, but is highly dependent on site specific weather conditions. |
New DVD teaches how to scout apple orchards |
Did you like the information in the article Apple scouting through the summer months in this issue of the Fruit CAT Alert? Learn more in A Practical Guide for Scouting Apple Orchards. The 90-minute DVD is divided into 21 modules covering topics from choosing a weather monitoring system to discussions on degree-day models and monitoring primary disease and insect pests. The DVD can be viewed in one sitting, but is designed more for those who want to learn about specific topics at any point during the growing season by simply choosing the desired tracks from the DVD menu. The DVD can be purchased through the MSU Extension
Bulletin office and some local Extension offices. Call 517-353-7640
or order on the Internet at: http://web2.msue.msu.edu/bulletins/
The DVD was produced with funds from the USDA with additional support provided by the Michigan Apple Apple Committee, MSU IPM Program, MSU Extension, the Michigan Agricultural Experiment Station and Project GREEEN. |
I've got fire blight in my orchard, now what? |
Conditions during apple bloom were conducive for fire blight infection in many parts of Michigan. We began seeing fire blight strikes the week of May 16-22 in Southwest Michigan. Following the intense thunderstorm trauma event of May 21 in Southwest Michigan with high winds and hail, we anticipate the development of additional fire blight strikes in approximately one to two weeks. This timing for symptom expression will probably be similar in the Fruit Ridge area and Southeast Michigan. Fire blight strikes can be separated into blossom blight strikes and shoot blight strikes. Blossom blight symptoms include blackening of the blossom, developing fruit and pedicel and leaf wilting (Photo 1) and are usually accompanied by droplets of ooze exuding from the pedicel. In a severe early-occurring blossom infection, all growth ceases, while in other cases, fruit will partially develop and will be changed into an inoculum factory, exuding large quantities of ooze droplets. Shoot blight strikes exhibit the classic shepherd's crook symptom, tissue wilting and blackening and can also be accompanied by ooze (Photo 2). Oozing fire blight strikes represent sources of bacteria that can continue to infect actively growing shoots, further spreading the disease. Existing strikes can also lead to persistent internal tree infections and canker development. Young trees on fire blight-susceptible rootstocks are also at risk for rootstock blight, which can kill young trees. Highly susceptible varieties (e.g. 'Gala', 'Jonathan') are at the most risk because these trees cannot slow disease development. See the variety table on page 47 in the 2004 Michigan Fruit Management Guide for a listing of varietal susceptibility to fire blight. Can anything be done to limit
the spread of fire blight within orchards once symptoms are seen? Pruning fire blight strikes should be done under dry conditions to minimize the chances of reinfection of the cut surface. The strikes should be pruned out as soon as they appear. Failure to do so increases the likelihood that blight will continue to spread both to adjacent trees and into the rootstocks of affected trees. Pruning cuts should be made at least 8 to 12 inches below visible symptoms because the fire blight bacterium is spreading internally within the tree. Pruning tools should be sterilized by dipping in a 10 percent bleach solution between cuts. Surface sterilization of tools prevents carryover of inoculum between trees. Be sure to change the bleach solution after a number of cuts as the bleach percentage gets diluted over time. Pruning out infections in mature trees may not be practical, but mature trees with a full crop will set terminal shoot buds earlier than young trees. When trees set terminal buds, blight stops spreading both between trees and within the affected trees. Remove strikes before the cankers extend into the tree. Trees must be examined at least two or three times weekly until the epidemic slows as tree growth slows. In sections where individual trees are severely affected, it may be more cost-effective to immediately remove entire trees, especially if trees are a susceptible cultivar like Gala. Pulling out badly affected trees will allow blight removal crews to focus their efforts on trees that can be salvaged. Blight removal crews should be trained to recognize the early symptoms of blight on terminal shoots. On terminals just beginning to show symptoms, the first or second fully expanded leaf will droop and closer examination will show blackening along the mid-vein at the base of the leaf blade (Photo 3). The shoot tip may appear to be slightly yellow or orange (Photo 4). Remove such shoots by cutting back into two-year-old wood at least 8 to 12 inches below the last visible symptoms. If a spur or shoot on the central leader shows signs of blight (Photo 5), remove the central leader down to 8 to 12 inches below the last visible symptom. Immediate and aggressive removal reduces the need for repeated pruning in the same tree and may result in fewer trees lost to root stock blight later in the season. Making cuts into at least two-year-old wood is a good strategy because the bacteria moves more slowly in older wood. Also, leave "ugly stubs" by cutting branches between nodes and at least several inches away from the central leader. Small cankers that form on these stubs can then be removed during winter pruning, whereas a canker that forms at a flush cut on the central leader will be missed during winter pruning. Prune during dry weather. An Extension specialist in California reported that he failed to transmit fire blight with pruning tools when he purposely made cuts through active cankers in dry weather. However, he succeeded in transmitting blight on pruning tools when pruning was done in wet weather. Blight removal operations should usually be suspended in wet weather, but that is not always possible. In an ideal situation, blight removal would only be done in dry weather. However, when a week of rain is predicted just as the first symptoms of blight appear, one must weigh the risks of spreading blight by pruning in wet weather versus the risks of giving the epidemic a full-week, or even a two- or three-day head start. With highly susceptible cultivars like Gala, remove blight as quickly as possible, even if that meant that some removal would be done in less than ideal weather. Should prunings be removed from
the orchard? The presence of cankers in trees is an important inoculum source as these cankers will produce ooze as temperatures warm. Pruning out strikes from a tree that also has several cankers will not effectively reduce existing inoculum in trees. The optimal timing for pruning out cankers is the dormant season. See the article in last year's CAT Alert (September 23, 2003 issue) discussing fire blight cankers. Also see Mark Longstroth's previous article on pruning out fire blight and other post-infection care available online at: http://web1.msue.msu.edu/vanburen/fbfight.htm |
Eutypa
dieback management focuses on cultural methods
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Symptoms Monitoring Biology
and management Control
should therefore focus on cultural methods, such as: 1) Removing large pieces of wood from
the vineyard to reduce inoculum pressure; 2) Burning wood piles as soon as possible, since they remain sources of ascospores, which can easily reach nearby vineyards; 3) Monitoring and tagging infected vines annually; 4) Pruning out infected canes or branches well below visible cankers or discoloration in the wood; 5) Renewal of trunks (except where the cankers extend below the soil line); 6) Removal and replanting of infected vines. Since symptoms take so long to develop, successful management of Eutypa dieback takes a concerted and continuous effort on the part of the grower. It
may also be difficult to decide when to remove or prune infected
vines, since yields are not seriously reduced until symptoms become
severe. As a rough guide, if you see 20 or more severely stunted
shoots on a vine, half or more of the fruit yield may be lost. Vines
nearly dead may produce no fruit at all or only a fraction of the
yield of a healthy vine. In the future, there may be other options for control, but at this time, the best management approach is to be vigilant and monitor vineyards at least once a year. If you are not sure whether you have Eutypa dieback, send a sample to a diagnostic lab or contact the Small Fruit Pathology program at MSU. We have developed a DNA-based method with which we can rapidly detect the fungus in infected vines. |
Section 18 label for Spartan 4F on strawberry in Michigan for 2004 |
The EPA has approved a Section 18 emergency label for use of Spartan 4F herbicide on strawberries in Michigan for 2004. Spartan may be applied at renovation from June 25-July 25, 2004, or at dormancy, after October 15 through December 15, 2004. Apply 4 to 8 fluid ounces of Spartan 4F (0.125-0.25 lb active ingredient) per acre per application. Apply in 20 to 40 gallons water per acre. A maximum of 12 fl. oz (0.375 lb ai) may be applied per acre per season. Spartan will control many broadleaves and grasses, including common groundsel, field pansy, mayweed chamomile, redroot pigweed, white campion (cockle) and yellow woodsorrel. It also will give some suppression of yellow nutsedge. The label should be available from chemical dealers, or may be downloaded from the vegetable AOE website, web1.msue.msu.edu/vegetable/. The label must be in the hands of applicators at the time of application. |
Stay on top of vineyard management |
Here are some of the features available for grape
growers at: grapes.msu.edu Coming later this summer: weed control information, and production recommendations from Dr. Stan Howell. |
Fertilizing after heavy rains |
Growers have questioned whether they should apply more fertilizer to compensate for nutrients leached out of the rootzone by recent heavy rains. The only nutrient to be concerned with is nitrogen (N). Soil N in the nitrate form is very mobile and leachable, so several inches of rain certainly can push nitrate beyond the reach of roots. However, perennial fruit crops get most of their N from soil organic matter and fertilizer applications are only a supplement. Warm, moist soils supply ammonium and nitrate to plants through mineralization of N in organic matter, so nitrate leached by rain is generally replaced through additional mineralization. This is why in most cases, I don't think more fertilizer is needed to compensate for nitrate losses. Additional N is justified in some specific situations. Generally, plantings on extremely sandy soils low in organic matter may benefit from additional N because these soils supply less N through mineralization. If all N was applied in one application, an additional application of 20% may be justified if a heavy crop of fruit is set. If the crop load is light, no additional N is needed. If growers use split applications and have already applied the first application, they can also increase rates in the last application by up to 20 percent if a heavy crop is expected. Again, do not increase N rates if the crop load is light. If additional N is going to be applied, consider which form is best. Urea is an inexpensive N source but is prone to volatilization. This means that if urea remains on the soil surface, N may be lost to the atmosphere as ammonia gas. Up to 40 percent of N applied, as urea may be lost under the worst conditions. Losses are generally minimal if: 1) more than 0.2 inches rain or irrigation follows applications to wash urea into the soil, 2) temperatures stay cool (below 75 degrees) until rain is received, or 3) soil pH is below 5.5. This means that urea may not be the best choice if the extended forecast is for hot, dry weather (and irrigation is not available). Urea may also be a poor choice for plantings that were just limed because the pH of the soil surface may be very high, which promotes volatilization. In these situations calcium nitrate may be a better source since nitrate is not prone to volatilization. Ammonium nitrate has intermediate volatilization potential since only half of the N in this source is ammonium. |
Regional reports |
1 - Southwest |
Weather
Tree fruit The selection of pesticides during rainy windy seasons can be difficult. Drenching rains will wash off protectant fungicides and insecticides such as Guthion and Sevin. A better choice would be systemic materials absorbed into the plant and not washed off by rain. Many of the newer fungicides are systemic, see the fungicide mode of action chart on page 17 of the 2004 Michigan Fruit Management Guide that groups fungicides as protectant and systemic. A few of the newer insecticides such as the neonicotinoids, such as Provado, Assail, Calypso, etc., Avaunt, and spinosad materials as well as others are systemic materials absorbed into the leaves and cuticle of the plant. See the Insecticide descriptions on page 18 in the 2004 Michigan Fruit Management Guide as well as the tables of effectiveness with the fruit sections for each crop. In peaches, flagging of peach shoot tips attacked by Oriental Fruit Moth larvae can be found. Plum curculio and tarnished plant bug damage can also be found on peach fruit. We are now catching both peach tree borers. In sweet cherries, early coloring fruit is dropping. Bacterial canker fruit symptoms can be found. Growers need to protect against brown rot, cherry leaf spot and plum curculio. In tart cherries, the high winds caused some damage in older orchards with broken limbs and blown down trees. Growers need to protect against brown rot, cherry leaf spot, and plum curculio. Plums are at pit hardening. Growers should be applying plum curculio and black knot sprays. White apple and potato leafhopper have been reported in the region and growers should protect young trees. Apple fruit set is variable and some varieties such as Red Delicious are scarce. Empire and others are set heavy and will require thinning. Because of the cool weather, thinning sprays will be less effective. We are at the end of the thinning window, so combination sprays at full rates should be used now. See the Growth Regulator section of the 2004 Michigan Fruit Management Guide for more information. We feel that primary scab season is over. Apple scab lesions are still appearing and secondary spread from these lesions is possible. Growers should maintain scab protection until they feel sure their orchards are clean. For apple scab infections from leaf lesions use the last column of the apple scab infection table on page 43 in the 2004 Michigan Fruit Management Guide. More scab symptoms should appear May 27. The May 27 symptoms will be from last infection at the end of primary apple scab ascospore production. Growers should scout their orchards for scab symptoms. Powdery mildew symptoms are becoming common in apples. Last week's stormy weather coincided with the appearance of fire blight blossom blight symptoms. We had as many as four fire blight infections during bloom and the first symptoms were found May 19 in Van Buren and Berrien counties. Thunderstorms with high winds and hail crossed the region on the May 21, 22, and 23. There is still scattered bloom in the orchards so these storms were infection periods. Many growers sprayed to prevent trauma blight and the further spread of the disease. The conditions are similar to those in 2000 but there were fewer infection periods during bloom in 2000. There are fewer acres of apples; especially young apples so hopefully this year will not be as bad. Wilting flower clusters and shoots can be found across the region. The full extent of the damage should be apparent in a couple weeks. Growers are applying and reapplying sprays for plum curculio, Oriental fruit moth and codling moth. There are still a few leafroller larvae feeding in terminals and fruit clusters. European red mite and aphid numbers are down after the heavy rains. White apple leafhopper and potato leafhopper have been reported in the region and growers should protect young trees. In pears frost rings are common on the fruit. In addition to those pests mentioned in apples, growers should also protect against pear scab. Pear psylla are scarce. Small fruit In grapes, flower clusters are separating in the bunch and wild grapes are blooming.
Concord bloom should begin late next week. Vineyards in low frost damaged areas have few secondary
buds and basal buds growing. Accurate yield estimates can be made
with the fruit buds visible. Broken shoots and tattered leaves
from high winds and hail are
easy to find. Windy, rainy weather has growers struggling to apply
fungicide sprays. Grape berry moth egg laying usually begins at
about bloom and rose chafer emerges to feed on the bloom. Include
insecticides in the final prebloom spray next week to control these
pests. Strawberries have thimble-sized fruit and some growers are harvesting off plastic beds. There is tarnished plant bugs damage to green fruit Raspberries and blackberries are blooming. Fall raspberries shoots are 10 to 12 inches tall. There are leafrollers working in raspberries. Orange rust symptoms are showing up. The wet conditions are perfect for this disease. Growers can reduce the spread of this disease with Nova but infected plants should be removed. Cranberries buds are swelling. Miscellaneous |
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2 - Southeast |
Weather Our soils
are now waterlogged, and spraying from the numerous infection periods
has become very difficult. There is puddling or standing water in
many low areas of fruit farms. There is a fair amount of soil structure
damage being done by the necessity of spraying operations. There
are now many ruts in orchards. Soil temperatures have now risen
to be consistently in the lower 70's. High wind conditions have
also made it very difficult for spraying operations to take place
in the breaks between thunderstorms. Many growers have been washed
clean three to four times over the last week.
Tree fruit New pests
in apples this week include Oriental fruit moth flagging, potato
leafhopper sightings, and some emergence of green apple aphids.
Oriental fruit moth trap catches have dropped off, and larvae have
been seen at several farms. The larvae have been tunneling into
the tips of shoots. I would encourage growers to particularly scout
their young blocks to make sure that Oriental fruit moth is not
the problem. Potato leafhopper are now being seen at a few farms.
This early batch of leafhopper are a concern and something we need
to watch fairly closely over the next two weeks. Plum curculio have
been seen in many blocks of fruit and have begun stinging apples,
sweet cherries, and other tree fruits. Codling moth trap catches
are generally down this week in the range of one to four per trap.
There are several larvae now in apples, these include red banded
leafroller, green fruit worm, eastern tent caterpillar, obliquebanded
leafroller and fruit tree leafroller. Most of the larvae are in
low numbers and fairly small size with the exception of green fruit
worm, where the larvae are larger. Tarnished plant bug have also
been seen feeding in apple as well as peach. There are a few eggs
from spotted tentiform leafminer, however it does not appear that
we had a strong flight or a high number of eggs from the first generation.
As mentioned earlier, green apple aphids are starting to show up,
however they are not cluster on terminals yet. Rosy apple aphids
continue to be seen in fairly low numbers. European red mite hot
spots continue with very few new hot spots showing up. Apple rust
mites also continue to be seen. San Jose scale adults are now being
caught in traps in Southwest Michigan, so I would expect them early
next week. There are good numbers of predators that have continued
to emerge over the last week; these include Stethorus punctum, velvet
mites, ladybird beetles, minute pirate bugs, and lacewings. Apple scab
spore discharge has decreased to a point where I am calling an end
to primary apple scab season as of this morning (May 25) rain event.
This is the earliest I have ever called an end to primary apple
scab. However, lesions
are just now starting to show at many fruit farms. I would encourage
growers to maintain fungicide sprays for at least another week to
determine the existence or the extent of apple scab in the orchard.
No fireblight has been seen. Pears continue to size quite nicely with most being around 14 or so mm in size.
Last week I reported a fairly good fruit set, however over the last
week I have been seeing a good deal of drop on most pear varieties.
Pear psylla is now under control at most farms, however where it
has not been controlled there are still very high numbers of psylla.
Growers should be looking for pear psylla adults at this time. Fireblight
shoot strikes have not appeared on pear. I would have expected symptoms
over the weekend if we were going to have them. However, keep an
eye closely on pear for fireblight strikes. Peaches are sizing very nicely across the region with most of them being around
16 mm in diameter. Oriental fruit moth (OFM) flagging of the tips
has been seen at a few farms. Scouting for OFM damage should take
place fairly quickly. Tarnished plant bugs have been found in peaches,
as have been a few plum curculio stings. We have not caught any
peach tree borers, but Southwest Michigan just started, and I would
expect to see them beginning to show up later this week or early
next week. Sweet cherries continue to size quite well with most being
around 12 mm in size. Pit hardening has not occurred. Bacterial
canker fruit symptoms are starting to show up. With all the rain
we have had, cherry leaf spot and brown rot need to be controlled,
and plum curculio is a continuing concern. Tart cherries are mostly around 10 mm in size. Again, growers
need to be protecting for cherry leaf spot and brown rot and keep
an eye out for plum curculio. Small fruit Fall red raspberries are now around 12 inches in length. Leafroller
damage is now being seen in several fall red raspberry patches.
I have not seen any raspberry cane borer damage, but I would expect
to see some beginning in the next week to ten days. Summer raspberries are now in early bloom across the region. Generally,
raspberries are looking fairly good where there was no tip damage
due to winter injury. Blueberries are ending their bloom at many farms across the region. We have an excellent
crop of blueberries this season. Scouting for cranberry fruitworm
and cherry fruitworm needs to continue. |
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3 - Grand Rapids Area |
Weather Degree days and precipitation are accumulated beginning January 1
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