Vegetables

Vegetable Crop Insects - Joanne Whalen, Extension  IPM Specialist;   jwhalen@udel.edu

 

Cucumbers.
All fields should be scouted for cucumber beetles and aphids. Fresh market cucumbers are susceptible to bacterial wilt, so treatments should be applied before beetles feed extensively on cotyledons and first true leaves. Pickling cucumbers have more tolerance to wilt, but a treatment may be needed if you find 2 or more beetles per plant and significant damage can be found on the cotyledons. A treatment should be applied for aphids if 10 to 20 percent of the plants are infested with aphids with 5 or more aphids per leaf.  Fulfill, Thionex or Lannate will provide aphid control. Be sure to watch for bees foraging in the area and avoid insecticide applications on blooming crops.  A pyrethroid, Lannate, Sevin or Thionex are labeled for cucumber beetle control in cucumbers.
 

Melons.
Continue to scout all melons for aphids, cucumber beetles, and spider mites. We continue to see an increase in the number of fields with spider mite infestations. If populations are high at the time of treatment, 2 sprays spaced 5 days apart may be needed. The threshold for mites is 20-30% infested crowns with 1-2 mites per leaf. Acramite, Capture, Danitol, Agri-Mek or Kelthane will provide control, but should be rotated to avoid the development of resistance. The treatment threshold for aphids is 20% infested plants with at least 5 aphids per leaf. Continue to watch fields carefully for cucumber beetles. Be sure to look under the plastic where beetles can often hide until disturbed. Be sure to watch for bees foraging in the area and avoid insecticide applications on blooming crops. 
 

Peppers.
Fields should be sampled for thrips and corn borers.  Although corn is growing rapidly and should be more attractive to corn borer moths, you should still watch for corn borer egg masses in isolated fields ( i.e. not near corn fields). You should also check local moth catches in your area (http://www.udel.edu/IPM/traps/latestblt.html ).  A treatment with a pyrethroid may be needed if corn borer moth catches exceed 10 moths per night, especially if corn planting is delayed in your area or you are using rye strips as windbreaks.  In general, 2 applications will be needed to achieve effective control.  Thrips can cause damage in peppers by vectoring tomato spotted wilt virus and by causing direct plant damage. There have been reports of tomato spotted wilt in tomatoes in  Virginia so watch fields carefully.  Although there are no available thresholds, a treatment may be needed if you see populations increasing. Baythroid, Capture, Spintor and Warrior will provide thrips control. In addition to thrips and corn borers, you should watch for aphids feeding on peppers. A treatment may be needed prior to fruit set, if you find 1-2 aphids per leaf for at least 2 consecutive weeks and beneficial activity is low.
 

Potatoes.
Colorado potato beetle (CPB) adults and larvae can be found in many fields, even where at planting treatments were used. The treatment threshold for adults is 25 beetles per 50 plants and defoliation has reached the 10% level. Once larvae are detected, the threshold is 4 small larvae per plant or 1.5 large larvae per plant. The threshold for each should be reduced if all stages of larvae are present.   Avaunt + PBO, Actara, cryolite, Spintor or Provado will provide control. Corn borer sprays will now be needed 3-5 days after an increase in trap catches. Be sure to check our website http://www.udel.edu/IPM/traps/latestblt.html) for the most recent moth catches in your area. Avaunt, Ambush, Baythroid, Furadan, Penncap, Pounce or Spintor will provide control. If you are scouting for infested terminals, the first treatment should be applied when 20-25% of the terminals are infested. Furadan or Monitor will provide the best control if you are waiting until you see infested terminals.  Economic levels of potato leafhopper adults and nymphs can be found in many fields. As a general guideline, controls should be applied if you find ½ to one adult per sweep and/or one nymph per every 10 leaves. Dimethoate, a  pyrethroid, Actara or Provado will provide control. 
 

Snap Beans.
All fields should be scouted for leafhopper and thrips activity, especially seedling stage beans. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. If both insects are present, the threshold for each should be reduced by 1/3. Dimethoate, Lannate, Asana, Capture, or Warrior will provide control of both insect pests. As soon as the earliest fields have buds present, a treatment will be needed for corn borer control once  moth catches are above 2 per night in your area. Be sure to check our website (http://www.udel.edu/IPM/traps/latestblt.html) for the most recent moth catches in your area.
 

Sweet Corn.
Flea beetles and cutworms are still active in seedling stage sweet corn. The treatment threshold for flea beetles is 5% infested plants. The cutworm threshold is 3% cut plants or 10% leaf feeding. We are also seeing cereal leaf beetle adults in seedling and whorl stage corn. A treatment may be needed if you find 10 beetles per plant and 50% of the plants exhibit damage. Continue to sample any corn in the whorl stage to pretassel stage for European corn borer larvae.  A treatment should be applied if 15% of the plants are infested. In recent years, Avaunt (whorl stage only), Baythroid, Mustang, Penncap, Spintor or Warrior has provided effective control. If economic levels of corn borers are present in pretassel to tassel stage corn, two sprays spaced 3-4 days apart are often needed. The first silk sprays will be needed for corn earworm as soon as ear shanks are visible. Treatment will be needed on a 5-day schedule.  

 

 

 

Bee Kills in Watermelons – Derby Walker, Sussex County Agricultural Agent, University of Delaware; derby@udel.edu

 

Bee kills in watermelons is a serious problem. Everyone loses when it happens. The bee keeper loses his bees and the grower loses the pollination service.  Unfortunately, materials act differently.  Some kill the worker bees in the field during spraying.  Others can be carried by the field workers from the field to the hive.  Larvae are then killed.  If the brood larvae are affected, you are looking at a 21 day set back before the queen will lay new eggs and new workers are available to care for the hive. It is economically important for growers to protect the bees that are in your field.

 

We recently looked at a field where most of field force was killed off. We think the hives will recover, but it will take time to replace the field force and build up the colony strength.  As a grower, you can help reduce the problem of bee kills by informing the bee keeper of when you are going to apply bee killing materials. Spray late in day when there are fewer bees in the field.  Alert the applicator to hive location to avoid direct spraying of hives.  Select the safest material that works. You can provide additional protection for the bee hives by sitting your overhead irrigation system over the hive and run the system while the field is being sprayed. Another trick is to soak burlap with water and cover the hives to keep them in and cool.  This would probably be the only way to protect hives sitting in the field. You have to remove the burlap right after spraying to prevent them from getting too hot and being killed by the heat. In the past, we used to just use local bee keepers. They could come protect their hives.  Commercial bee keepers cannot make it around to all of the sites to protect their bees. A lack of bees will cost growers quality and yield. Can you afford not to help protect them?

 

Vegetable Crop Diseases - Bob Mulrooney, Extension Plant Pathologist, University of Delaware, bobmul@udel.edu

 

Late Blight Advisory

 

Disease Severity Value (DSV) Accumulation as of June 2, 2004, is as follows:

Location: Joe Jackewicz Farm, Magnolia, DE. Greenrow: April 25, 2004

 

Date	Daily DSV	Total DSV	Spray Recommendation
4/25- 5/2	4	4	none
5/3	8	12	none
5/9	2	14	none
5/13	1	15	none
5/17	2	17	none
5/18	1	18	none
5/19	4	22	7-day
5/20	2	24	7-day
5/21	2	26	7-day
5/25	5	31	7-day
5/27	3	34	7-day
5/30	8	42	7-day
5/31	1	43	7-day
6/1	1	44	7-day

 

All potatoes in DE have accumulated 18 DSV’s or more by now. The threshold of 300 P-days was also exceeded yesterday, which would recommend initiating sprays for early blight. This will be important for growers with early blight susceptible varieties. This 300 P-day threshold was exceeded for potatoes that emerged on or before April 25.

 

Growers who do not want to rely only on the DSV calculations for scheduling fungicide applications should apply mancozeb (Dithane, Pencozeb, Manex II) or Bravo before plants canopy down the row and repeat on a 7-day schedule. Late blight has not been a problem here in Delaware for many years and unless you have seed from an unknown source, the risk of late blight is very low.

 

 

Management Strategies for Phytophthora Fruit Rot Control in Pickling Cucumbers -

Bob Mulrooney, Extension Plant Pathologist, University of Delaware, bobmul@udel.edu

and Ed Kee, Extension Vegetable Specialist, University of Delaware, kee@udel.edu

 

 

Phytophthora fruit rot can be a devastating disease of pickles on Delmarva. Last year’s wet season was a very favorable year for Phytophthora capsici on many crops. The fungus is soilborne and the overwintering oospores can remain viable in the soil for 10 years or more. Cultural practices that help control Phytophthora are (1) as long a rotation away from susceptible crops (tomatoes, peppers, eggplants, lima beans, cucurbits including pumpkins, summer and winter squash, watermelon, and cantaloupe) as possible, (2) plant only well-drained fields,  (3) use as wide a row spacing as possible to allow drying and reduce humidity. Properly constructed raised beds can also be helpful as they keep vulnerable plants from saturated soil conditions. The most effective control measure that growers have available is to avoid planting in infested soil and limit the spread of the disease to clean fields. Fungicides have also been shown to provide some control if applied at the right time and good coverage is achieved. A combined approach of all available control methods is more effective than using just one control measure.

 

Recent work done in Michigan by Dr. Mary Hausbeck and her team over the past several seasons to control Phytophthora fruit rot has promise for us here in Delaware. We have relied on applications of Ridomil Gold or Ultra-Flourish in a band at planting followed by several applications of Acrobat or Gavel combined with a copper fungicide such as Champ or Kocide for

fruit rot control. Their research is showing the best control under their conditions with three applications of Acrobat or Gavel when fruit are

  

1, 3, and 5 inches long. Under our conditions, fruit may size so quickly that only two sprays at

1 and 3 inch long fruit would be used here. Application of the fungicides is also very important. All the fungicides for fruit rot control which includes Acrobat, Gavel (zoxamide plus mancozeb), mancozeb (Dithane DF, Manzate, Penncozeb) and copper hydroxide (Champ, Kocide) are not systemic, so coverage of the fruit is very important if control is to be effective. It is not enough to just spray until the leaves are wet, you need enough pressure and/or air to drive the fungicide to the fruit. They have had good success with conventional spray rigs equipped with 8003 nozzles, spaced 20 in. apart operating at 60 psi, delivering 30 gal/A. Air-assisted sprayers with 4 nozzles spaced 60 in. apart, delivering 10 gal/A have also been demonstrated to be very effective.

 

Fungicide test plots and large demonstration plots have shown that several treatments have proven effective under varying amounts of disease pressure. As mentioned before, Acrobat 50 WP (6.4 oz/A) or Gavel 75DF (2 lb/A) are applied with 2 lbs. of Kocide or Champ when they are applied. They are getting slightly better control compared to the untreated check by alternating Gavel with Acrobat. Since Gavel contains mancozeb it has a 5 day pre-harvest interval (phi) which limits its use close to harvest. They were applying Gavel at the 1 and 3 in. stage and ending with Acrobat at the 5 in. size. There was no significant difference between all three sprays of either Acrobat or Gavel.

 

All that being said, we would recommend for Delaware growers that they choose their fields wisely following the non-chemical guidelines add