June 11, 2008

In this issue

§ Vegetable insect update

§ Recent rains favor Phytophthora development on vegetable crops

§ Potato late blight risk forecasting and potato disease extension bulletins

§ Fungicide application opportunity for the control of Rhizoctonia and black dot in potatoes.

§ Regional reports

§ Weather

Vegetable insect update

Beth Bishop
Entomology

Aster leafhoppers collected last week from celery fields in southwest Michigan and carrot fields in Oceana and Mason counties were tested by Diagnostic Services for aster yellows infection. Four different leafhopper samples were tested and none of them carried aster yellows. This means that the risk of aster yellows is low at this time, and treatment thresholds are high (50 aster leafhopper per 100 sweeps for carrots, 35 aster leafhopper per 100 sweeps for celery and 25 aster leafhopper per 100 sweeps for lettuce). Aster leafhopper numbers throughout Michigan have been, in general, lower than this threshold, although recent strong storms may have brought more into the state. Growers should regularly scout susceptible crops. We will continue to test leafhoppers for aster yellows infection since new populations may have different infectivity rates.

The first flight of European corn borer moths is underway. The number of European corn borer moths caught in pheromone traps in Monroe, Macomb, Ingham, Lenawee, Washtenaw and Mason counties the week of June 3-10 increased substantially compared with the previous week. We do not have accurate numbers because storms over the weekend dismantled many of the traps. Most sweet corn fields are not at risk for European corn borer damage. Moths prefer larger plants to lay eggs on (field corn is generally more attractive than sweet corn this time of year) and young corn borer caterpillars do not survive well on small corn plants. In general, treatment is only required prior to tassel emergence if 15 percent or more of the plants are infested with corn borer larvae during the whorl stage.

We set up corn earworm traps on campus last Tuesday, June 3.. They were blown down by the storms over the weekend, and set up again on Monday, June 9. On Tuesday we had 14 corn earworm moths in one trap and 42 in another. Corn earworm does not overwinter in Michigan and these undoubtedly moved in on the recent weather fronts. Vegetable crops are only vulnerable to corn earworm infestation when fruiting (tomatoes, beans) or silking (sweet corn), so these moths pose little threat. However, this does show how weather can quickly bring large numbers of insect pests into the area. Again this year, researchers Mike Sandstrom and Dave Changnon at Northern Illinois University are issuing “insect migration forecasts” based on weather. These are issued on weekdays throughout the growing season and each “forecast” gives predictions for 1 day, 2 days, and 3-5 days from today. You can access the insect migration forecasts through this website: http://www.agweather.niu.edu/IMRFForecast.html.

Recent rains favor Phytophthora development on vegetable crops

Mary Hausbeck
Plant Pathology

Phytophthora on asparagus

Several diseases limit asparagus production. Phytophthora spear and root rot is favored by excessive rainfall and poor soil drainage. The disease results in soft, water-soaked lesions and shriveling on shoots and roots, curving of spears, and loss of root mass and vigor. The rains received in many regions of the state during the last week are comparable to those of 2004. In the spring of 2004, after excessive rainfall during spear harvest, a spear and root rot was observed in several asparagus fields in Oceana, Ingham and Van Buren counties. Ridomil Gold EC or Ultra Flourish are labeled to manage Phytophthora spear rot. Label instructions include application 30 to 60 days before the first cutting and another application just before harvest in a minimum of 10 gallons of water. The Phytophthora asparagi from Michigan is sensitive to mefenoxam , which is the active ingredient in both Ridomil Gold EC or Ultra Flourish. Fosphite, Phostrol, and Prophyt are also labeled for use on asparagus, but I’ve not seen any data on their effectiveness in protecting asparagus from spear rot. Although the damage from Phytophthora on the spears is obvious, the damage to the crown is seen by poor fern growth and reduced yield the following year. Once the crown becomes infected by Phytophthora it will not recover and cannot be cured. Growers can expect the longevity and productivity of their fields to be seriously compromised from Phytophthora infection.

Phytophthora on vine crops

Michigan growers producing vine crops have reported significant losses due to Phytophthora blight in recent years. The pathogen responsible is Phytophthora capsici. Recognizing disease due to P. capsici is not always easy, as the disease often occurs in the low areas of a field where water accumulates. Many growers assume that when plant stunting occurs in these sites, it is due to the water logging of the roots, but infection by P. capsici may be to blame. Under conditions of standing water, P. capsici produces swimming spores (zoospores) which can move about in water and cause infection of nearby plants. Squash and pumpkin plants often have obvious symptoms of plants wilting or collapsing prior to dying. Such plants often have brown to black discolored roots and crowns. The disease is easily seen on infected fruit, initially as dark, water-soaked lesions which then develop a distinctive white, “powdered sugar” layer of spores on the surface of the fruit. Fruit infection is especially troublesome because the infection may occur days before the symptoms become visible. As a result, healthy-appearing fruit may be harvested and then shipped. Fruit then break down during transit or on grocers’ shelves resulting in disposal cost.

To control P. capsici several control measures need to be implemented. Good drainage is important in managing this disease. However, even plants growing on well-drained fields on raised beds may have severe disease if rainfall is heavy. Crop rotation may reduce the number of P. capsici spores remaining in a field. A minimum of three years crop rotation to hosts other than those listed in Table 1 is recommended to avoid build-up of P. capsici. Growers should avoid relying on a single fungicide for disease control in order to delay development of fungicide resistance with P. capsici. There are many fields in Michigan where the P. capsici has become resistant to the commonly used fungicide, Ridomil Gold (mefenoxam). Fungicide programs including the following may provide disease management: Acrobat 50WP (6.4 oz), Gavel 75DF 1.5-2.0 lb, Tanos 50WG (8-10 oz). Fields heavily infested with P. capsici may require the use of pre-plant fumigation for disease control. Fumigants that are most effective include: Telone C35, Vapam HL, and Sectagon 42. Trial results from a new fungicide, Presidio (fluopicolide), appears promising and may complement a spray program that includes other Phytophthora fungicides.

Control of Phytophthora is complicated by its broad host range, long-term persistence in agricultural soils, presence in irrigation water sources, and ability to develop resistance to fungicides. An integrated production system combines cultural methods and tolerant cultivars, effective fungicides and use of uncontaminated irrigation sources.

Table 1.Common vegetable hosts affected by Phytophthora capsici.

cucumber	summer squash	zucchini	hot pepper	snap beans
gourd	watermelon	eggplant	tomato	yellow wax beans
pumpkin	winter squash	bell pepper	lima beans

Table 2.Products tested in Phytophthora trials.

Product	Active ingredient	Labeled
Captan 80WDG	captan	no
Forum 4.16SC	dimethomorph	yes
Gavel 75DF	zoxamide/mancozeb	yes
Presidio 4FL	fluopicolide	registration pending
Previcur Flex 6EC	propamocarb	yes
ProPhyt 4.2EC	phosphorous acid salts	yes
Ranman 3.6SC	cyazofamid	yes
Reason 4.13SC	fenamidone	yes
Revus 2.08SC	mandipropamid	no
Ridomil Gold MZ 76.5WP	mefenoxam/mancozeb	yes
Tanos 50WG	famoxadone/cymoxanil	yes

Potato late blight risk forecasting and potato disease extension bulletins

Willie Kirk and Phill Wharton
Plant Pathology

Recent weather events have elevated the risk of potato late blight development throughout the Michigan potato-growing regions. Growers in all areas are now recommended to apply fungicides at maximum labeled rates and to consider late blight activity of fungicides being used to control other diseases. Daily updates of potato late blight risk and updates on extension meetings held throughout the state, are available for all the MAWN sites in Michigan at http://lateblight.org Other issues are also regularly updated on this site.

High-resolution potato diseases extension bulletins are now available for purchase from the MSU Extension Bulletin Office for $1.50 each. The new group of publications includes the recent potato late blight bulletin and bulletins on early blight, pink rot, fusarium dry rot, rhizoctonia diseases, potato common scab, white mold and seed piece management. In addition, pocket scouting guides for disease are available for purchase.

For more information, call 517-353-6740. You can also download these bulletins from the “Extension publications” page as pdf files from the website http://lateblight.org.

Fungicide application opportunity for the control of Rhizoctonia and black dot in potatoes

Willie Kirk
Plant Pathology

Recent weather conditions may have been suitable for the development of Rhizoctonia diseases and possibly black dot if weather conditions become hot in the next few days. Results of trials across the United States suggest that black dot may be suppressed by an application of a strobilurin or similar fungicide, such as Quadris, Evita, Headline, or Tanos, prior to canopy closure. The objective of this application is to get the fungicide onto the lower stem and into the tuberization zone of the soil. Results from work we have done at MSU also suggest that some supplementary control of Rhizoctonia disease can also be attained from this timing with this group of fungicides. Applications should be made prior to scheduled irrigation which helps drive the fungicide into the critical zone.

Regional Reports

1 - SW Michigan Research and Extension Center

Ron Goldy

Weather

Temperatures were generally above normal for the period with lows from 61°F to 71°F and highs from 77°F to 88°F. There was accumulation of 1.5 to 3.0 inches of rain across the immediate area. Those receiving 1.5 inches are back irrigating and those receiving 3.0 inches are having difficulty getting in their fields.

Crop report

Asparagus harvest is complete and growers are applying post harvest herbicides and fertilizer.

Peas are at early harvest.

Sweet corn is now 14 to 16 inches tall.

Pepper and eggplant transplanting is mostly complete.

Final tomato planting will occur this week. Early planted, non-tunneled tomatoes are in bloom. Staking, tying and suckering of tomatoes continues.

Vine crops have responded well to the warm temperatures. Harvest will begin next week on early planted, tunneled fields of yellow squash and zucchini.

Pumpkins are being planted

2 – Grand Rapids Area

Bill Steenwyk

Weather

Water water everywhere! This phrase sums up our experience in the counties surrounding Grand Rapids. The most intense storms and heaviest rainfall occurred in the southern half of Ottawa and Kent, along with the northern half of Allegan and Barry counties, where many locations received five to seven or more inches on June 6 through 9. Some locations received more than five inches just from the storm on the night of Saturday, June 7. Soil texture, topography and drainage systems were key determinants of crop survival.  A grower on very sandy soils near the Holland lakeshore area reported no standing water and only minor seedling loss, despite receiving six to seven inches in a single storm event. By contrast, I called a muck grower who was surveying his celery field from a rowboat!
Crop report

Crops on the upland, mineral soils fared pretty well, with the exception of low spots. Some of the longer or steeper slopes eroded and lost plants along with soil. Crops were killed and are dying in the lower, more poorly drained areas of fields. Overall, however, the sweet corn, cabbage, tomato, peppers, beans, peas and vine crops are in good condition. 
Muck crops are quite another story.  Those grown on organic soils in Allegan, Kent and Ottawa counties have been adversely affected, but not uniformly. Celery on one farm is expected to be nearly destroyed, while only ten miles away, another farmer reports that nearly all of his will survive if additional weather or pest stress does not occur while the plants recover. The condition of drainage ditches streams and surrounding land use was very important. Where weeds and brush impeded drainage, or where surrounding development channeled more water into the streams, the fields would not drain adequately. In one case, pump failure helped convert a field into a lake.
The radish, celery, onion, lettuce and potato crops have been all been damaged with radish being hit the hardest by far.  Red beets have been stressed, but appear likely to recover.  Crops such as sweet corn, tomato and squash growing on muck soils have also been adversely affected.  In another week, I will have a clearer picture of how well each crop has fared.  
I urge all growers in this area to be checking fields regularly for signs of nutrient deficiency, weed escapes, and disease pressure.  In the past, I have witnessed the loss of fifty lbs nitrogen per acre from denitrification and leaching which occurred as a consequence of a single five inch rain event. Muck soils can lose potash. Herbicides have been lost from the weed seed germination zone, and many growers will be unable to get back on the fields for a while to apply post-emergent controls.  Where plants survive, we need to continue the watch for root and crown rots as well as other diseases.
Note that the photos in this article represent some of the more severe conditions. While some are like them or even more severe, other fields have not been impacted as badly as depicted in the images and will recover to differing degrees.

3 – Oceana County

Norm Myers

Weather

Oceana County experienced heavy rains over the last week. Most people received from four to five inches, with some reporting over six inches from last Thursday (June 5) through yesterday morning. No hail was reported, but there is flooding in low parts of many fields. Growers are worried about fertilizer and pesticides applied prior to the rain being washed away or leached out of the root zone.
Crop report

Cooler temperatures have made it easier to keep up with the asparagus crop, but growers are facing new problems with sand-splash and especially purple spot. Phytophthora can also be seen in wet areas and along the margins of wet areas. Loss of pre-harvest fertilizer and a big flush of new weeds are also concerns. Common asparagus beetle is a problem in some fields when the weather warms up. Growers hope to pick late this year since they are only a little past half of last year’s tonnage.

There was some serious flooding in carrot fields. Most growers will be out of the fields for up to a week and that could interfere with weed control operations. The few fields that have been swept for aster leafhoppers have seen a jump in numbers since the rains. Stands are generally thinner than growers would like to see and they are more worried about aster yellow damage than in a more normal year.

Planting of both processing zucchini and jack o’lantern pumpkins was in full swing when the rains hit and most people will be out of the fields for at least a week before planting can resume. Loss of curbit and furadan are a concern in both of these crops.

European corn borer traps are set. Most sweet corn is behind where it should be for this point in the year.

Earliest plantings of snap beans have now emerged.

4 – Mason-Newaygo counties

Jim Breinling

Weather

After the dry period, the rainfall continued during the past week. Precipitation has been recorded at the Fremont Enviro-weather station on seven of the first ten days of June. The total for June at Fremont is 3.79 inches and 3.93 inches at Ludington. Most of the rainfall occurred on Sunday, June 8 with 2.04 inches at Fremont and 2.37 inches at Ludington. When wet follows dry, it is shown more dramatically, where at Fremont 4.65 inches has fallen during the last 13 days compared to .89 inches received during the first 29 days of May.

Temperatures have been above normal during the past week, but not as warm as reported in other areas of the state. The high during the week was 83.8°F at both the Fremont and Ludington stations.

Crop report

Carrot planting was scheduled for completion this week in Newaygo County.

Onion plantings observed in Newaygo County on Friday, June 6 were approximately eight inches tall. Cover crop kill has been accomplished and hand weeding had begun in some fields.

Spinach plantings were responding well to the moisture and warm temperatures with excellent growth.

Stripped cucumber beetles were found on June 6 in two cucurbit plantings. One planting was an organic grower. The other planting had not received an insecticide application at planting.

The extensive rainfall in Mason County is of concern where squash fields were just planted.

Potato fields have responded well to the improved growing conditions and exhibit little damage due to the previous freezing temperatures. Colorado potato beetle reported in instances where no insecticides have been applied.

European corn borer trap counts on June 9 at the snap bean site in Mason County were 5-0- 6. The zero catch in trap 2 was due to the trap being down.

The corn earworm and western bean cutworm traps will be put up on June 16 at the sweet corn site in Mason County.

5 – Macomb, Lapeer, St. Clair counties

Hannah Stevens

Weather and crop conditions

Weather conditions have been dynamic this week with maximum temperatures ranging from 67°F to 92°F, damaging winds of 50 MPH on Sunday, June 8 and a total of 1.8 to 2.7 inches of rainfall in the three-county-area this week. Some areas received some precipitation every day this week with most of it in the past three days. I’m certain I will be hearing of more collapsed barns and downed trees and utility poles in the next few days. Fieldwork has essentially been on hold for the past three days. Crop growth was dramatic in all commodities.

Crop reports

The early potato crop, grown on plastic for retail sales, is robust and beginning to flower.

Onion thrips have been reported in sweet onion transplants. While onion maggot flies have been present all season, we have seen no damage.

The early fields of cabbage are beginning to head up and look spectacular (view photo). Cabbage maggot injury has been reported from one site.

Cool soil temperatures resulted in poor establishment of the first several plantings of fresh market snap beans, but the later plantings are emerged and doing well. I suspect potato leafhoppers are in beans and potatoes at this time.

Sweet corn is being planted as field conditions permit. European corn borer trap catches jumped this past week with an average of 12 per trap. The crop growth was impressive this week with corn standing 1-2 feet tall and of good color. Stands are variable with the earliest plantings having had some emergence problems. I have walked several fields and have seen an occasional corn flea beetle and some feeding damage, but only one plant with possible bacterial Stewart’s wilt.

The muskmelon and watermelon crop is beginning to run under plastic row covers. A little heat stress in the form of marginal leaf burn can be seen in some areas.

Striped cucumber beetle has appeared on squash, pumpkins and cucumbers.

There was remarkable growth in the past two weeks in tomatoes with the earliest planting setting fruit and second earliest being tied with the first flowers appearing. Growers in the more northerly areas of the region waited to plant until early last week. High tunneled and greenhouse tomatoes are beginning to show color.

6 - Monroe County

Sudeep Mathew

Weather

According to the MSU Enviro-weather in Dundee we have received a total rainfall of 1.49 inches this week. Amounts I have heard from individuals range from 0.50-inches to 1.81 inches. This rain will positively impact the growth of many vegetables in the area. Field temperatures were in the rage of 65°F-91°F. For the first entire week of this growing season, soil temperatures did not drop below 60°F which has greatly improved growth of vine crops.

Crop report

Sweet corn is progressing to the silking stage (Photo 1) in some early planted crops on tunnels and is looking forward to being ready for July 4. European corn borer was found in our traps and averaged 13 moths per trap. It was interesting to see seed corn root maggots on seed treated sweet corn roots.

Early planted cabbages started under tunnels were continuing to be harvested in some fields. Cabbage root maggots and diamond back moth activities were found at several fields. Many growers made an insecticide application this week. Cabbages are showing some fungus symptoms resembling those of phytophthora.

Peppers were looking good after the much needed rain.

Cucumbers are well adapted to the rain and responding well. Dr. Mary Hausbeck’s downy mildew spore traps monitoring system (Photo 2) has been placed in the area. This will help growers in early detection of downy mildew to make informative decisions.

Market tomatoes staking is going on. Leafhoppers were found at a tomato field.

Potatoes are beginning to blossom. Low numbers of potato leafhoppers were found. I have not seen any Colorado potato beetle in the field yet.

Weather news

Jeff Andresen
Agricultural Meteorology
Geography

Severe weather slams region

Several rounds of severe thunderstorms brought heavy rains, strong winds, and hail to many sections of Michigan (and other sections of the Midwest) on a daily basis from June 6 through June 9, causing widespread property damage and loss of power for thousands. The thunderstorms brought widespread rainfall to the state, with totals since last Friday generally ranging from less than one inch in far northern and southern sections of the state to more than six inches in some west central counties. While increasing the risk of foliar disease, the rain greatly eased or ended problems with dryness that had intensified during recent weeks. The severe weather outbreak across the Midwest was associated with meandering frontal boundary and an unusually hot, humid air mass in place across the region, strong wind shear (increasing winds with height), and a series of upper air disturbances moving southwest to northeast across the region. On a statistical note, the severe weather outbreak kept the United States on pace to approach or set a new record for the greatest number of tornadoes in a calendar year.

An area of high pressure across the northern United States is expected to bring a fair and dry weather pattern to Michigan through early Friday. A cold front will approach from the west late in the week, however, bringing the likelihood of more showers and thunderstorms in far western sections of the state by late Thursday or early Friday and across most sections by Friday afternoon or evening. Given that somewhat similar synoptic conditions to last weekend are expected to be in place by Friday, more severe thunderstorms will be possible. Fair and dry weather is expected following the frontal passage on Saturday and Sunday. Temperatures during the next few days will jump back to above normal levels, with highs Thursday and Friday generally ranging from the mid- to upper 70s north to the upper 80s or low 90s south and lows from the low or mid- 50s north to the mid- or upper 60s south. Somewhat cooler temperatures are a good bet by Saturday and Sunday.

Further ahead, the medium-range forecast guidance generally calls for the formation of upper air troughs across western and eastern sections of the United States with an upper air ridge expected across the Great Plains. This would leave Michigan and the Great Lakes region in northwesterly flow aloft, which typically translates to cooler and drier than normal weather conditions. The official National Weather Service 6-10 day and 8-14 day outlooks covering June 16 through June 20 and June 18-24, both call for mean temperatures across Michigan to fall to below normal levels and for near normal precipitation totals.