Vegetables. Volume 11, Issue 22 August 22, 2003

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1 Volume 11, Issue 22 August 22, 2003 Vegetables Vegetable Insects - Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu Cabbage. Be sure to sample fall planted fields for diamondback and cabbage looper larvae. We can find both insects in fall cabbage fields. The treatment threshold is 5% of the plants infested if both species are present, Avaunt (3.5 oz/acre), a Bt, Proclaim (3 oz/acre), or Spintor (4-5 oz per acre) will provide control. If cabbage looper is the predominant species, a pyrethroid, Intrepid (8 oz/a) or Confirm (8 oz/acre) will also provide control. Lima Beans. As soon as pin pods are present, scout fields for lygus bugs and stinkbugs. Treatment should be considered if you find 15 adults and/or nymphs per 50 sweeps. Lannate, Capture or Warrior can be used if both species are present. A higher rate of Capture (4 oz/a), Mustang (4.3 oz/a) or Warrior (3.84 oz) will be needed if stinkbugs are the predominant insect present. Corn earworm can now be easily found in lima bean fields. A treatment is recommended if you find one worm per 6 foot of row. Materials labeled for earworm control include Capture, Mustang MAX, Lannate and Warrior. Peppers. At the present time, all peppers that have fruit ½ inch in size or larger should be sprayed on a 5-7 day schedule for beet armyworm, corn borer, corn earworm, and fall armyworm. If you still plan to spray Orthene or Address (acephate), they will not provide satisfactory earworm control. A pyrethroid or Lannate will need to be combined with acephate for earworm control. Lannate or a pyrethroid will not provide effective beet armyworm control. Avaunt, Spintor or Intrepid will provide the best beet armyworm control. Depending on the pest complex present, a combination of products will be needed. Snap Beans. Orthene or Address (acephate) should be applied at the bud and pin stages on processing snap beans for corn borer control. A pyrethroid should also be added to the pin spray for corn earworm. After the pin spray, sprays will be needed on a 5-day schedule until harvest. Since this can change quickly, be sure to check our website for the most recent trap catches and information on how to use this information to make a treatment decision in processing snap beans ( and our link to h.html). As soon as pin pods are present, fresh market beans should be sprayed on a 5 to 7-day schedule. Lannate, Capture, Mustang MAX or Warrior should be used. Weekly Crop Update 1

2 Spinach. As soon as plants emerge, fields should be scouted for webworm and beet armyworm larvae. Controls should be applied when worms are small and before they have moved deep into the hearts of the plants. Also, remember that both insects can produce webbing on the plants. Since beet armyworms are more difficult to control, chemical selection is important. Confirm, Intrepid or Spintor will be needed for beet armyworm control. If webworms are the predominant species, Ambush, Pounce, Confirm (6-8 oz/acre), Intrepid (8-10 oz/a) or Spintor (4-8 oz/acre) should be used. Generally, at least 2 applications are needed to achieve control of webworms and beet armyworm. Sweet Corn. Fresh market silking sweet corn should be sprayed on a 2-3 day schedule throughout the state. Be sure to check our website for the most recent trap catches and information on how to use this information to make a treatment decision in fresh market sweet corn ( and tml ). UD IPM Black Light and Pheromone Trap Counts Average Number of Moths per Night: August 15 to August 18, 2003 Trap Location Kent County European Corn Borer Black Light Corn Earworm Black Light Corn Earworm Pheromone Trap Dover Harrington Killens Pond Little Creek Milford Rising Sun Wyoming Sussex County Bridgeville Concord Georgetown Greenwood Laurel Seaford * Numbers can change quickly. For the most recent trap counts, access the website at ( or call (in-state); (out-ofstate). Counts are updated on Tuesday and Friday. Vegetable Crop Diseases Bob Mulrooney Extension Plant Pathologist; bobmul@udel.edu Downy Mildew Alert on Cucurbits. Downy mildew on pumpkins was seen in Kent County this week. Downy mildew can defoliate pumpkins quickly under favorable weather conditions. Look for small angular yellow spots on the upper surface of the leaves. In the early morning, you can see the small tufts of grayish fungus on the corresponding lower surface of the leaf. Be sure you are spraying on a 7 day schedule with Bravo, or Acrobat. You can also apply mefanoxam in combination with Bravo (Flouranil, Ridomil Gold/Bravo), mancozeb (Ridomil Gold/MZ) or copper (Ridomil Gold/Copper) every 14 days and apply Bravo or maneb on the alternate weeks. Weekly Crop Update 2

3 Plectosporium blight (Microdochium) is also present on the stems, petioles, leaves, and a few fruit. This disease infects pumpkin and squash. Look for the numerous, small, white to tan colored crusty spots. This can cause vines to die early as well as infecting the fruit and making it unmarketable. Bravo will control it as well as programs that are alternating Bravo with Cabrio, Flint or Quadris. Thorough coverage is very important for good control. In most years, a regular fungicide program which included Bravo provides control of Plectosporium on the fruit, but this year may be different. Be sure to keep up your fungicide spray program. Virus diseases are appearing in pumpkins as well. Look for dark green mosaic symptoms, strapping of leaves and distorted growth. These viruses are aphid transmitted and cannot be controlled at this time. Watermelon mosaic virus 2 (WMV2) is usually the most prevalent here on Delmarva. Planting resistant varieties is the best plan of control, but there are few available at the present time. Unknown virus (probably WMV2 on pumpkin Plectosporium on stem and petiole Mosaic symptom of pumpkin virus infection. Plectosporium on immature pumpkin Powdery mildew on curcurbits is increasing and growers are reminded to keep up their sprays schedules. Apply Bravo plus Nova or Bravo plus Procure alternated with Cabrio, Flint or Quadris. Weekly Crop Update 3

4 Vegetable Diseases Kate Everts, Extension Plant Pathologist, Univ. of MD and Univ. of DE; Powdery mildew on pumpkin leaf. Peppers. Phytophthora blight on peppers has been diagnosed this week. The crown rot phase will cause plants to wilt. Look for white to cream colored fungus growth on the stem near the soil line. The roots are not infected. The fungus progresses and can develop into an aerial phase there stems and fruit are infected as well. Ridomil or Ultra Flourish can be used as a directed banded soil application on either side of the plant to help control the crown rot phase. To check the stem and fruit rot stage apply Ridomil Gold/Copper at 2.5 lb/a every days. Be sure to check the label for restrictions. If the weather is very favorable for disease (lots of rain) and the disease is present, fungicide control may be disappointing. To prevent in the future, plant on raised, domeshaped beds and apply Ridomil or UltraFlourish in the trickle system when using plastic mulch. Lima Beans. White mold was seen this past week in baby limas. Keep up sprays of Topsin M or Rovral if you have had a history of white mold. Downy mildew has not been seen as of this writing. The predicted high temperatures for Friday will negate any prediction for downy mildew, but the showers and cooler weather following the cold front will put us back in downy mildew weather again. Be sure to keep up applications of copper on beans that have flowers, pins and/or pods. Powdery Mildew on Cucurbits Powdery mildew is present at high levels in the pumpkin crop. Resistance to Quadris and other strobilurin fungicides (Cabrio, Flint, etc.) was detected in several areas around the U.S. in This year Quadris does not appear to be performing well in my trials. This could be an indication that resistance is present here on the Delmarva Peninsula and that strobilurins will not give as good management of the powdery mildew pathogen as they did in the past. A conference on disease resistance, sponsored by Syngenta, was held in July. An excerpt of the conference can be heard on the internet at the following site: =1149&C=0 To manage powdery mildew most effectively, always follow good resistance management guidelines. Begin with disease free transplants or certified seed. Apply fungicides at label rate (don t cut the rate). Alternate a strobilurin with a product that has a different mode of action. Keep on a good spray schedule (a 7-day interval for powdery mildew). Be sure you are getting good fungicide coverage of your plants. Do not apply more than four applications of a strobilurin. Be aware of products that are at risk for resistance development. A list of registered products and fungicide class, including their risk level for resistance development is in the Delaware Extension Bulletin 137 and the Maryland Extension Bulletin 236 on page E24. Weekly Crop Update 4

5 Field Crops Field Crop Insects - Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu Soybeans. At this point, we are starting to see diseased green cloverworms and it appears that populations have started to crash. However, if populations were high last week and you did not treat, be sure to check fields one more time. The threshold prebloom is 30% defoliation. Once fields begin to bloom, the threshold is 15% defoliation. The pyrethroids and Lorsban will provide good control of cloverworms. Soybean Aphid Watch We continue to see an increase in soybean aphid populations especially in New Castle County, but aphids can be found in fields in all 3 counties. We have also found a few fields with economic levels in New Castle and Northern Kent Counties. We still believe that these populations have migrated on wind fronts from the Midwest. As you remember, we reported our first find in New Castle County in mid-july (one month earlier than 2002). Weather conditions continue to be favorable for aphid development and beneficial activity is still low in many fields. Data from the Midwest indicates that the greatest benefit from an insecticide application occurs from the late vegetative stage to R2 (full flower) stage. However, there is also data showing a yield advantage from treating through R4 (full pod) in years with adequate moisture. In our area, the R4 stage can last up to 3 weeks. So, the critical time for treatment is from the late vegetative stage or the initiation of bloom to early pod-set. Current guidelines from the Midwest say treat if you find aphids per plant on 80% of the plants in a field or 25 or more aphids per leaflet. Early in the season, aphids tend to be located on new growth. As vegetative growth stops, aphids will move down the plant to leaves lower in the canopy and to stems and pods. On later planted fields, treatments should not be applied too early to avoid recovery of populations and the need to reapply treatments during the risk window from R1 through R4 growth stages. The following products are registered and have provided effective control in trials in Minnesota and other states in the Midwest: Asana, Baythroid, Furadan, Lorsban, Mustang MAX, Penncap-M, Pounce and Warrior. The midhigher range rates should be used to achieve the best results. Dimethoate has a 2ee registration; however, in these same trials it has not provided the level of control provided by the pyrethroids and other labeled products at 4 DAT (85 versus 99% control). Trials in the Midwest also show the pyrethroids tend to provide longer residual control. However, they also state that with limited immigration into a field any labeled product might provide effective control. Good results have been obtained with moderate water (15-20 gallons) and pressure (35-45 psi); however, in 2002 aerial application (5 gpa) provided control equivalent to ground applications. Reports on yield returns from insecticide applications have been as high as Bu/A; however, if economic levels are present and beneficials do not crash populations, the yield advantage in insecticide treated fields has averaged 6-8 bushels per acre. The conditions necessary to crash populations would be a period of hot, humid weather. With the forecasted cooler weather at the beginning of next week, aphid populations could continue for a longer than normal period. Predators are generally more effective at higher temperatures and fungal diseases are most effective when we see prolonged periods of hot, humid weather. Although many fields may never reach economic levels, all fields should be checked to avoid losses from this insect pest. You should also scout the earliest planted fields as soon as blossoms are present for corn earworm. Low levels of corn earworm and a few beet armyworm have been found in fields in Sussex County. Since weather conditions will determine if populations increase or crash, it will be Weekly Crop Update 5

6 important to scout fields to determine when and if a treatment is needed. Although we generally see our greatest outbreaks in drought stress years, soybeans may be more attractive in areas where corn has brown silks, plants have started to dry down and soybeans are blooming. The treatment threshold for corn earworm is 3 per 25 sweeps in narrow fields and 5 per 25 sweeps in wide row fields ( 20-inches are greater). The following materials will provide corn earworm control in soybeans: Ambush, Baythroid, Asana, Mustang MAX, Pounce, Warrior (all pyrethroids) Steward, or Larvin. If beet armyworm is present, Steward would be the preferred material. It now has a 2ee label for use on soybeans in Delaware. Lorsban also provided good beet armyworm control in Grain Marketing Highlights - Carl German, Extension Crops Marketing Specialist; clgerman@udel.edu Commodity Markets Turn Volatile on Fund Activity, Weather, and Crop Conditions. USDA lowered crop condition ratings this week with U.S. corn down 5 points in the good/excellent category, now at 60% nationwide. Soybeans took a similar turn, down 6 points, to 56% good/excellent. The condition ratings (reported Monday afternoon), fund activity, and uncertainty concerning weather developments has taken commodity markets higher for the second time this week. December '03 corn is now trading at $2.35, Nov soybeans at $6.82, and Dec wheat at $3.85 per bushel. Rain is needed in the heart of the corn belt to avoid yield losses, particularly in Illinois and Iowa. Expectations are for trading in the commodity pits to follow the weather forecasts in the near term. Marketing Strategy. A good rain in the central corn belt could send commodity prices spiraling much lower, while continued crop stress in principal growing areas could take Nov soybeans over the $6.00 mark, and Dec corn to $2.50/bu. or better. Therefore, it is important to consider rewarding market rallies with both corn and soybean sales, getting preharvest sales of both crops to the 50% level of intended production. Weather Summary Weeks of August 15 to August 20, 2003 Rainfall: 2.18 inches: August inches: August 17 Readings taken for the previous 24 hours at 8 a.m. Air Temperature: Highs Ranged from 89 F on August 15 to 78 F on August 19. Lows Ranged from 70 F on August 15 to 62 F on August 20. Soil Temperature: 79 F average for the week. (Soil temperature taken at a 2 inch depth, under sod) Web Address for the U of D Research & Education Center: Compiled and Edited By: Tracy Wootten Sussex County Extension Educator - Horticulture Cooperative Extension Education in Agriculture and Home Economics, University of Delaware, Delaware State University and the United States Department of Agriculture cooperating, Robin Morgan, Director. Distributed in furtherance of the Acts of Congress of May 8 and June 30, It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, sex, disability, age or national origin. Weekly Crop Update 6