July 20, 2005
In this issue
§ Honey bees and cucurbit pollination
§ Onion thrips numbers increasing in onions
§ Watch for striped cucumber beetles and western corn rootworm adults
§ Aster leafhoppers and aster yellows
§ Keep an eye on European corn borer
§ Economics and strategies to produce the highest quality tomato fruit
§ Regional reports
§ Weather news
Honey bees continue to be plaqued by a number of pests and diseases. Varroa mites (Varroa destructor) continue to be the worst pest of honeybees and cause high mortalities during fall and winter. Varroa mites, together with the viruses they carry (and inject into honey bees during feeding), have killed over 50 percent of honeybees nationwide during the winter of 2004. While individual beekeepers can experience up to 100 percent winter mortality in northern States (such as Michigan, Wisconsin and Maine), the national average is always about 10 to 20 percent. In 2005, California almond growers, which require 1.2 million colonies for pollination each year, took the hardest hit. Some paid about $100 per hive for pollination, compared to the usual $60 per hive. Others imported bees for pollination from Australia.
The varroa mites are largely resistant to ApistanÒ (a pyrethroid), which has been used for more than a decade. They are also starting to become resistant against CheckMite+Ò (an organophosphate), registered as a Section 18 (emergency registration) in most states (Michigan included) for the last four years. A new chemical, Api Life Var, became available (also Section 18) for varroa treatment in 2003. Api Life Var is composed mainly of Thymol and a few other essential oils, and its efficacy against the mites varies from 70 to over 90 percent. We encourage beekeepers to rotate pesticides (Apistan, CheckMite+, Api Life Var) as well as combining control with other integrated pest management (IPM) tactics, such as screened bottom boards, drone brood trapping of mites, etc, to delay the onset of resistance development in mites. Using IPM will also help reduce residual chemical levels in honeybee colonies. Alternative treatments such as a fungus that attacks Varroa and the Mitezapper (http://www.mitezapper.com) are still in development.
Another beekeeping concern is American Foulbrood, a baterial disease on bee larvae that can also kill colonies. The pathagen (Bacillus larvae) for this disease has largely become resistant to Terramycin (Oxytetracycline) and new antibiotics are in the process of being registered. The small hive beetle, a recently introduced pest from Africa, is also present in Michigan, but so far does not cause large damages if it is controlled in the honey houses. Michigan currently (per 2005 USDA statistics) has 65,000 bee colonies, a large drop from the 97,000 in 1995-1997, mainly due to more complicated management schemes to control the varroa mite. Pollination prices, so far, have not been affected because a large number of pollinating colonies come into Michigan from the southern States. While we were surprised to find some apple growers paid as low as $35 per colony for pollination spring of 2005, the price for cucurbit pollination will be higher ($50-70 range). This is because the raised bee price last spring did not have time to affect the apple growers (who used mostly beekeepers moving their bees back from the south), and also honey bees usually do not do well in terms of honey production or population increase when placed in cucurbit fields. In fact, most experience population decrease. The main reason might be cucurbits do not produce enough nectar or to sustain honeybee population growth.
Most cucurbit (cucumber, squash, melon) flowers have the following features: females and male flowers are separate, pollen are large, heavy and sticky, therefore require insects for transfer. Most importantly, most flowers are open for only one day, and unpollinated female flowers will abort and drop off if pollen is not received from male flowers on that same day. Each seed in a cucurbit requires one viable pollen, so a pumpkin with 500 seeds will need at least 500 grains of pollen. Good pollination produces better-looking products (even, not curled or mishaped), higher yield and better quality of fruit (e.g. higher sugar concentration). Due to pesticide use and habitat destruction, native bees (e.g. squash bees, andrenid and sweat bees), while more efficient for cucurbit pollination, are usually not of sufficient quantity to ensure adequate pollination. For pickle cucumbers, honeybees are crucial because most varieties now are gynoecious (mostly female flowers with another variety to provide pollen) and mechanical harvest requires quick fruitset and more even ripening. Honeybee colonies should be moved into the field or on its border two to three days before the first females flowers are to bloom.
For squash and melons, at least one colony per acre should
be used. For pickles, we recommend at least one colony per acre for
hand-harvested fields and two to three colonies per acre for machine-harvested
fields. Hand-harvested fields require fewer colonies because of the lower
number of flowers open in the field at any given time and that the field is
harvested several times. More honeybee colonies are required for a
machine-harvested field because there is a limited time for pollination to
occur to ensure that the fruit is of a uniform size when harvested. If you are
not sure whether there are enough bees in your field providing pollination, use
the following table. This table was developed specifically for pickle cucumbers
but should also be applicable for squash and melons.
To use the numbers in the table, you must observe 10 flowers for 10 minutes in three different locations (30 flowers per 30 minutes) and compare your findings to the table for the particular time of day you do your counts. If your bee counts are less than those found in the table, you need more bee colonies.
|
Number of honey bee visits for time of day (Eastern Daylight Time) |
Minimum number of bees per 30 flowers per 30 minutes |
|
8-9
AM |
1 |
|
9-10
AM |
3 |
|
10-11
AM |
9 |
|
11
AM - Noon |
13 |
|
Noon
- 1 PM |
16 |
|
1-2
PM |
13 |
|
2-3
PM |
11 |
|
3-4
PM |
7 |
|
4-5
PM |
5 |
Daytime sprinkling irrigation of vine crops will reduce yield by discouraging honeybee visits. Bees do not like to get wet while in flight, they also will avoid visiting flowers filled with water. In addition, too much water getting into the flowers will also disrupt pollen germination. For these reasons it is better to sprinkle the crops at night or early in the morning before honeybees are actively foraging, or use drip irrigation.
Fruit growers want to maximize
fruit production and beekeepers want to maintain their colonies healthy and
productive. Sometimes there can be a conflict between the two when bees are
placed in orchards for pollination and spraying is needed for disease or pest
control. Because bees are insects, most insecticides will have some toxicity to
bees, so close cooperation is needed to protect bees against poisoning among
growers, pesticide applicators and beekeepers.
Sometimes it becomes inevitable
that you have to spray while bees are still in the field. If you have to spray pesticides
during bloom, choose a liquid form over a dust form. Because bee morphology has
been designed to maximize pollen collection (size similar to dusts), pesticides
applied as dusts are more hazardous than sprays to honey bees.
Micro-encapsulated pesticides are worse because bees sometimes mistake these
granules for pollen and bring them home, causing long-term, chronic damage to
the entire colony. Spray of pesticide directly (e.g. ULV) is more toxic to bees
because of its higher concentration. Aerial application of pesticides is bad
news because many bees in flight will be hit. Time of application can be
important because many foragers will die when sprayed pesticides land on bees
directly or mix with nectar and bees forage on it. Consider working with your
beekeeper on the spray schedule. Give them some options considering the
chemical sprayed and the schedules of both the grower and beekeeper. For
example, tell the beekeeper a spray is really necessary, but you are concerned
about his bees. "Should I spray tonight 7:00-9:00 PM, when bee activity is
minimal; or do you think it is better to close the colonies tonight and spray
tomorrow morning 7:00-9:00 AM, and then release the bees around noon?” This
type of discussion will often lead to satisfactory comprise for both sides. It
does not cause any harm to bees for the colonies to be closed for a few hours.
During a very hot day, overheating can be an issue, but can be avoided when
water is provided abundantly (Use soaked burlap to clog the entrance and apply
water every two hours in July to September.).
Using a specific pesticide
targeting the pest you want to control is often better for you (less harm to
other beneficial insects) and for the beekeeper. Most pesticides are labeled as
not toxic, moderately toxic or highly toxic to honey bees. A list of pesticides
of low, moderate and high toxicity, as well as considerations for both growers
and beekeepers, can be found online at: http://ohioline.osu.edu/hyg-fact/2000/2161.html
Onion thrips numbers are increasing and may be at damaging levels in some onion fields. Onion thrips lay eggs in the leaf tissue, have two larval stages, pupate in the soil and emerge as adult thrips.
Treatment is recommended if numbers reach 10 to 15 thrips per plant. The eggs and pupae are protected from insecticide sprays, so sprays may need to be repeated at five to seven day intervals. Lannate has given the most consistent control in recent years, but growers should alternate with other products, such as pyrethroids, to reduce the potential for build-up of resistance. Heavy rains can be a major mortality factor, so fields should be re-scouted after rains, before applying insecticide.
Striped cucumber beetles (see photo) are a major pest of vine crops because they transmit bacterial wilt disease. Vine crops growers may also see western corn rootworms feeding on pollen in flowers. They look very similar to striped cucumber beetles but western corn rootworms do not transmit bacterial wild and are not a pest of vine crops. Both beetles are striped, pale yellow or beige and black. Legs of the striped cucumber beetles are light colored; legs of the western corn rootworm are dark colored. Also, the cucumber beetles will generally have lighter colored stripes and be more yellow than beige; the western corn rootworm's stripes are beige or tan.
Adult western corn rootworms can be a serious problem in sweet corn, if numbers are high enough to cause significant silk clipping. Damage can be especially high in fields adjacent to field corn. Growers should check sweet corn fields as they begin to silk to be sure damage is not occurring. If silks are turning brown, pollination has already occurred and silk feeding will no longer cause a problem. Most products used for control of European corn borer and corn earworm will also control western corn rootworm adults.
To complete the corn rootworm/cucumber beetle family photo album, the spotted cucumber beetle is also called the southern corn rootworm and is rarely common enough to be a pest in either crop. The northern corn rootworm is pale green/gray; it's more common in northern Michigan, as its name suggests and is rarely found in vine crops.
If treatment is needed, Michigan State University Extension
bulletin E-312, Insect, disease, and
nematode control for commercial vegetables, is available on the web at:
http://web4.msue.msu.edu/veginfo/bulletins/E312/index.htm
Bulletin E-312 is also available in hard copy from your
local MSU Extension office or from the MSU Bulletin office at: http://web2.msue.msu.edu/bulletins/mainsearch.cfm.
Product labels and material safety data sheets are available at http://www.cdms.net/pfa/LUpdateMsg.asp
Aster leafhopper numbers increased during the past week in some areas of southwestern Michigan. Tests of leafhoppers collected from a few celery fields in this area show that very few of these leafhoppers are infected with aster yellows. These leafhoppers may be young adults either recently emerged from the immature (wingless) stage, or recently blown in from the south on weather fronts. Because these results are from a limited number of fields, we recommend a conservative estimation of 3 to 5 percent infectivity. This infectivity rate translates into a treatment threshold of 7 to 10 aster leafhoppers per 100 sweeps for celery.
We have few new results of aster leafhoppers collected from carrot fields in Oceana, Mason and Newaygo counties. Infectivity rates of aster leafhoppers from this area have been higher throughout the season than those collected from southwestern Michigan. In general, most samples processed since early June have shown infectivity rates of 5 percent or more. The treatment thresholds corresponding to the most current infectivity rates range from 3.5 to 7 aster leafhoppers per 100 sweeps for susceptible varieties of carrots.
Very few moths were caught in traps during July 12-19. In south and central Michigan, we have accumulated just enough degree days (base 50) for the second flight of moths to begin (1450 to 1500 degree days). We expect moth flight and egg laying to begin in much of Michigan in the next week or so. Once it does, corn in tassel and beyond, and peppers and snap beans with fruit should be protected from European corn borer by insecticide applications.
The highly variable weather this summer is one of the chief factors influencing fruit quality in fresh market tomatoes, and if it continues during the period of rapid fruit expansion, it could cause substantial damage. Micro-crack defects such as “shoulder check” and fruit cracking can greatly reduce marketability and storage life of tomato fruit. Cracking defects tend to be substantially higher if the period of fruit expansion coincides with precipitation that follows periods of hot, dry weather.
Improving nutritional status of tomato plants is one way that growers can address fruit quality at its root, by insuring a consistent supply and balance among nutrients to support even expansion of the fruit. Fertigation is a widely used practice to supply nutrients throughout the fruit filling period. Growers often experiment with different ratios of nitrogen to potassium in the fertigation solution. Our experiments conducted in southwest Michigan indicate that fine-tuning the nitrogen to potassium (N:K) ratio can be critical to producing high quality fruit on different soil types. In most cases, a ratio of 1N:1K during fruit fill was the best ratio and was consistently associated with high fruit yields. However, at sites where fruit cracking or shoulder check was a severe problem then a higher level of potassium (a ratio of 1N:2K) provided the firmest fruit and lowest crack incidence, in comparison to 1N:2K and 1N:3K (Snapp and Huang, 2004). The highest level of potassium tested, a ratio of 1N:3K, did not improve fruit yields or fruit quality in our research.
The bottom line for potassium nutritional enhancement is that it is not usually profitable to add more potassium above the recommended level of a 1:1 Nitrogen to Potassium ratio in fertigation systems (Table 1). The exception may be for sites where fruit cracking is a severe problem. In such cases, growers may want to experiment with moderately higher potassium to nitrogen ratios, as this is a proven means to improve fruit firmness.
Improving nutrition through spraying calcium and boron at the green fruit stage is another promising method for enhancing fruit quality. Calcium sprays have often shown inconsistent benefits in our studies, but the increase in fruit quality with a supplemental boron spray (weekly over the fruit filling period) has shown consistent results at the Southwest Research and Extension Center near Benton Harbor (Snapp and Huang, 2004). The economic net benefits have been calculated to be $230 to $340 per acre, comparing the increase in yield of high quality tomatoes to the cost of applying boron (Table 1). Boron is a micronutrient that should not be over applied. Applied in excess, it can cause physiological defects. Do not apply more than 0.25 pounds per acre of actual boron per foliar spray and be cautious of multiple applications of boron. There are a large number of fertilizer sources of boron on the market, such as Borax.
Some tomato producers are also trying high tunnels, which can markedly increase the level of high quality fruit produced, but this is an expensive technology to implement. It is important to redesign fertilization strategies for tomatoes produced under high tunnels. On the one hand, the fruit yield will generally increase substantially in a high tunnel environment and thus require sufficient nutrition, but on the other hand, vegetative growth may also increase excessively and reduced levels of nitrogen should be considered early in the growing season.
|
Year |
Fertilizer treatment |
Tomato benefit (dollar/ha)Z |
Fertilizer costs (dollar/ha)Y |
Net benefits |
|
|
Boron |
|
|
|
|
2002 |
|
2550 |
11.46 |
222.54 |
|
2003 |
|
4703 |
14.34 |
328.22 |
|
|
Potassium |
|
|
|
|
2002 |
|
|
|
|
|
|
1N:1.7K |
-3969 |
71 |
-55.89 |
|
|
1N:2.5K |
2062 |
142 |
14.52 |
|
2003 |
|
|
|
|
|
|
1N:1.7K |
-6017 |
71 |
-84.74 |
|
|
1N:2.5K |
-9251 |
142 |
-65.14 |
Z: Increased benefits as
compared to non boron spray (for boron) or 1N:0.8 K fertilizer treatment.
Y: Extra costs from non boron
spray or 1N:0.8K fertilizer treatment.
Snapp, S.S. and J. Huang. 2004. Optimizing fruit quality in fresh market
tomato. Michigan State University Extension Bulletin. E2927 (New)
It has been generally hot and dry. High temperatures ranged
from 85o to 90oF and lows 68o to 74oF.
Precipitation in the area was zero to 1.5 inches for the week. SWMREC continues
to be substantially below normal in precipitation with only 5.22 inches since
March 1.
Yellow squash, zucchini and cucumber harvest continues with few problems. Growers should watch for squash bugs.
Cantaloupe, watermelon and pumpkin growth is excellent. Some watermelon fields have mites and cantaloupe harvest will begin soon.
Tomato harvest has begun from tunneled fields. Some fields have mites and blossom end rot can be found.
Eggplant and peppers are growing well and harvest should begin this week. Warm weather is causing blossom end rot concerns in these two crops.
General sweet corn harvest has begun from early plantings. Some fields have twospotted spider mites. Growers need to assess the need for control based on harvest times.
Hot conditions have growers concerned about later planted fields maturing too soon and not staggered as planned. The weather may also increase blossom end rot symptoms.
Rainfall amounts on Saturday, July 16 were extremely variable from none in western Mason County to 2.5 inches reported at Grant in southeast Newaygo County. Only 0.29 inches were recorded at the MAWN weather station near Fremont. Temperatures have remained at or above normal during the past week.
In general, all vegetable crops continue to do well.
Snap bean harvest will begin in the area next week. Moisture is critical now for pod development and yield in early plantings. Crop potential looks good with no reported insect, disease or virus situations. All later plantings emerged rapidly and are growing well at this time. I’ve heard a couple of isolated reports of root rot and one replant situation due to heavy rain. There have been no European corn borer or corn earworm in traps this week.
Vine crops continue with good growth. Some weed control and stand problems. Most of the poor stands were reported in pumpkins. There have been some reports of cucumber beetles, but overall I have found very little cucumber beetle activity.
Sweet corn harvest will begin in Mason County this week.
We have had no rain in the last week and irrigation has resumed in most areas. We have not had the serious drought that other areas have had, at least since the end of June, so non-irrigated crops look better here than they do to the south.
In asparagus, new fern looks very thin because of phytophthora damage last year, but height and growth looks better since the rains resumed. Tom-Cast sensors have taken a big jump over the last week because of the high temperatures, high humidity and heavy dews. We are nearing the point of needing a second spray for purple spot. Common asparagus beetle activity has been about normal so far.
In carrots, scouts are now finding Alternaria as well as Cercospora leaf blights. We are getting just enough leafhoppers that at the present low thresholds, we need to spray every week to control them.
Growers are seeing some phytophthora in infected summer squash fields, but otherwise no serious disease problems yet. No virus yet. Some early processing zucchinis were picked last week, but the main harvest of the processing crop will begin later this week.
Rainfall was received this week throughout the region although it varied from a half inch in the north, where it remains dry, to a reported 3 to 4 inches on the east side of Macomb County. The heat has been impressive on several days and the rainfall as well as heavy dew has resulted in foliage being wet for 11 to 14 hours a day.
Early
plasticulture corn is beginning harvest while most early corn will be starting this weekend
or early next week. This signals the opening of the many farm markets and
retail movement of many vegetable crops. Very little first generation corn
borer damage has been reported on early corn. Hopefully this picture will not
change as harvest begins and keen eyes are watching for worms. I believe most
growers did not treat for first generation. Trap counts are up slightly this
week and I expect this signals the beginning of second generation activity.
Judging by my sweet corn plots the earliest plantings seem to be a week to 10
days behind the predicted days and it seems as if early and mid season
plantings will be bunching up.
Harvest of tomatoes has
started in the early fields. Thankfully, we have few problems with blossom end
rot or bacterial disease present on the fruit, but pressure from fungal disease
is heavier as of this date, and it would be appropriate to begin fungicide
applications. Many materials that are effective against early blight, Septoria
leaf spot and anthracnose may be applied with zero days to harvest. Consult
Extension bulletin E-312 including the web version at: www.msue.msu.edu/vegetable
Squash volume is heavy but the wholesale market is reported to be slow. Muskmelon and watermelon continue to grow rapidly, aided by the recent
rains.
Thrips
pressure is increasing but the onion crop looks excellent.
In snap beans, harvest is well underway at this
time with good wholesale movement reported. Leafhopper pressure is a potential
concern.
A vegetable growers
dinner program has been scheduled
for Tuesday, July 26 at 6:30 PM at the UAP Great Lakes warehouse in Imlay City.
Production issues concerning carrots, onions, lettuce and squash will be
discussed with MSU specialists Beth Bishop, Bernie Zandstra and Ryan Bounds.
Questions on other vegetable crops may also be entertained.
So that we may have
program materials and dinner for you, please give me a call at 586-469-6440 by
Monday morning, July 25 if you plan to attend.
A Sweet Corn Variety
Trial Open House and Program has
been scheduled for Wednesday, August 17, 3:00-6:00 PM at the George Van Houtte
Farm, 14381 33 Mile Rd, Bruce, Michigan, 48065. Participants will be able to
see and taste up to 17 varieties of super sweet and 15 varieties of SE’s.
The farm is north of
Romeo between Powell and M-53. Look for the MSUE Extension sign on 33 Mile Road
in front of the plots. Road construction has changed access to 33 Mile in the
past year or so. For more information, including directions, a list of
varieties or other questions, please phone 586-469-6440 or e-mail stevensh@msu.edu
Most of our area received about an inch of rain over this last weekend with some areas getting a bit more. Crops have responded to this with immediate growth. Degree days (base 50) have now reached 1500 for the season.
Sweet corn is being harvested with volume increasing each day. Quality looks good but growers are in the second and third planting with the first still not ready for harvest. No corn borer adults were in traps this week, even though we have reached the 1500 GDD level.
Market tomatoes are being harvested on a limited basis with larger volume by the weekend. This week I have seen several fields with bacterial canker (See photo) and also early blight. Several growers have reported tomato hornworms this week. Fruit set looks to be very good with reasonable size, considering the growing conditions.
Processing tomatoes have filled between the beds in early fields and filled the beds in later fields. Flowering of this crop looks tremendous with good fruit set apparent in early fields. Fields look clean of insects and diseases.
Muskmelons will be harvested late this week from fields tunneled and next week from non-tunneled fields with plastic mulch. Fruit size and shape looks good. Fruit set appears to be down a little from the last several seasons.
Pumpkins and squash are running vines and flowering with female flowers this week. Squash bugs and a few aphids are in fields. No diseases found yet in this crop.
Slicing cucumber harvest continues with growers in the fourth picking or more and quality looking good. Cucumber beetles are still active but in lower numbers than earlier in the season. We are in the middle of hand-harvest pickles now with good yields and quality.
Potato harvest has begun by a couple of growers for market. Vines are still very green and tubers very immature making it difficult to maintain quality in the package.
Pepper harvest is still a week or more away with fruits developing large size but still in need of wall thickness. Aphids have been found in this crop this last week for the first time this season. Most finds have been single insects with very few colonies developed yet. Fields appear to be free of diseases.
Cabbage harvest continues with growers planting for fall crops of this and cauliflower where irrigation is available and now in other fields following the recent rains.
A subtle but distinct change in the upper air pattern across the Great Lakes region is currently taking place, with the riding pattern of much of the past few weeks gradually being replaced by west to east (zonal) or even weak northwesterly flow patterns. While warmer than normal weather is likely to continue for next week or so (We’re currently at the warmest period of the year climatologically.), humidity levels will be less than in recent weeks and there will be more frequent chances for rainfall.
In the short term, a weak cool front will approach and pass through Michigan overnight Wednesday and Thursday (July 20-21), setting off some scattered showers and thunderstorms. Precipitation totals will likely remain in the 0.25- to 0.50-inch range where rain falls, with some isolated 0.5- to 1.0-inch totals possible on Thursday across sections of the Lower Peninsula. Warm, dry weather is expected over most areas of the state Friday and Saturday, with another frontal passage and the chance for showers and thunderstorms again on Sunday continuing into early next week. Similar to Wednesday night and Thursday, areal coverage of precipitation will likely remain on the scattered side, with some areas remaining dry. High temperatures during the next couple days will range from near 80 in northern areas of the state to near 90 in the south, with lows ranging from the mid 50's north to mid or upper 60's south. Slightly cooler temperatures are likely by early next week, but mean values will remain a few degrees above normal. The NOAA Climate Prediction Center 6-10 day (for July 25th-29th) and 8-14 day (covering July 27th-August 2nd) outlooks both call for weak upper air ridging across western sections of the country with mostly west-east zonal flow across the east. In the 6-10 day time frame, temperatures and precipitation totals are both forecast to range from near normal levels across the Upper Peninsula to above normal across the Lower Peninsula. Near normal temperatures and precipitation totals are forecast statewide during the 8-14 day period.