Vegetables

 

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

Cucumbers.
Continue to scout 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. If spider mite populations are high at the time of treatment, 2 sprays spaced 5 days apart may be needed. The threshold for mites is 20-30 percent 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 percent 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.
In areas where corn borer trap catches are above 2 per night and pepper fruit is ½ inch in size or larger, fields should be sprayed on a 7-10 day schedule for corn borer control.  If fruit is not present, larvae hatching from egg masses will feed on the leaves then move into the petioles and stems. For these fields, a pyrethroid application should be considered especially if egg masses are found and trap catches are above 10 per night in your area.

Correction to the Vegetable Recommendations for Acephate(Orthene) on Peppers.
If you read the current Orthene 75S label (as well as all current acephate labels), European corn borer control (ECB) is only listed under bell peppers and the rate is 1-1.33 lb per acre of Orthene 75S (not 0.67-1.33 as listed in the book). After talking to Valent, it appears that ECB was mistakenly dropped from the non-bell pepper label. The current  label states aphid control only at a rate of 0.67 lb/acre.(Orthene 75S).  Another difference is the maximum amount allowed on each pepper type (bell versus non-bell). Regardless of the formulation (Orthene 97, Orthene 75S or generic acephate), the maximum amount allowed for bell peppers is 2 lb ai/a/season. On non-bell peppers the maximum amount is 1 lb ai/a/season. Valent Corporation ( manufacturer of Orthene 97) has agreed to submit a 2ee label to EPA for DE,MD, NJ, PA, and VA to add corn borer back on the Orthene 97 label for non-bell peppers at a rate of ¾ - l lb per acre.  With this label change, you will be limited to one Orthene (acephate) application for corn borer control on non-bell peppers.  We will let you know when we receive the 2ee label.

Potatoes.
Continue to scout fields on a weekly basis for Colorado potato beetle (CPB) adults and larvae. The treatment threshold for adults is 25 beetles per 50 plants and defoliation has reached the 10 percent level. The larval threshold is 4 small larvae per plant or 1.5 large larvae per plant. The threshold for each should be reduced by 1/3 to 1/2 if all stages are present.   Avaunt + PBO, Actara, cryolite, Spintor or Provado will provide control. 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. Once corn borer catches reach 2 per night, fresh market and processing snap beans in the bud to pin stages should be sprayed for corn borer. Acephate  should be used at the bud and pin stages on processing beans. Once pins are present on fresh market snap beans and trap catches are above 2 per night, a 7-10 day schedule should be maintained for corn borer control.  Lannate, Asana, Capture, Warrior or Mustang are labeled.  Acephate has a 14-day wait until harvest. 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.
All silking sweet corn should be sprayed on a 4-5 day schedule.

 

 

 

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

 

Belly Rot on Pickling Cucumbers.
This fungus disease of the fruit is an often frustrating disease to prevent. The causal fungus Rhizoctonia solani is very common and can remain viable in the soil for many years. It has a very large host range and rotations are not very effective in control of Rhizoctonia. The optimum temperature for infection is 81°F and high humidity under dense foliage also contributes to favorable conditions for fruit infection. Rotations away from cucurbits can help as well as deep plowing before planting to bury the fungus. The most favorable conditions for belly rot are usually in July and early August following an early crop of pickles. Unfortunately fungicide control has always been inconsistent. The only labeled control is applications of Quadris or Amistar at the four leaf stage and again at flop or vine tip-over. This application timing requires another application in addition to any fungicide sprays for Phytophthora fruit rot control. (See last weeks newsletter for info on Phytophthora fruit rot control.)

 

 

Potato Disease Advisory.

 

Disease Severity Value (DSV) Accumulation as of June 9, 2004 is as follows:

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

 

Date	Daily DSV	Total DSV	Spray Recommendation
4/25- 5/18	4	18	7-day
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
6/4	17	61	5-day
6/7	2	63	5-day
6/8	1	64	5-day

 

The period beginning late June 4 and continuing through the 5^th, 6^th and the 7^th produced 61 continuous hours of humidity above our threshold. This produced the big jump in DSV’s. Hopefully, you will be able to apply a fungicide for disease control as soon as possible.

 

The seven day spray schedule is probably the most practical for growers although the model is calling for a 5-day spray interval at this time.

 

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.

 

Early Blight and Black Dot.
Many fields are flowering or approaching flowering and this is a good time to consider switching to an application or two of Gem, Headline or Quadris (Amistar) for early blight susceptible varieties. This can also be helpful for late season varieties including russets if stress makes plants susceptible to black dot. Make one or two applications at the end of flowering and repeat 14 days later.

 

If pink rot control is important and you did not treat at planting, foliar applications of either Ridomil Gold MZ or Ridomil Gold/Bravo, or Flouronil when tubers are nickel-sized is suggested.  A second application should be made 14 days later.  For specific fungicide recommendations, see pages F132-33, 2004 Delaware  Commercial Vegetable Production Recommendations Book. EB 137.

 

 

 

Hollow Heart of Watermelons – Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu

 

Watermelons have grown a lot in the past 10 days, growers are now beginning fungicide

sprays, scouting for insects and mites, and applying nitrogen.  While there is no special reason to anticipate any excess hollow heart problem, it is a good time to discuss what can cause this physiological problem.  Chris Wein, of Cornell writes,  “This disorder is characterized by the separation of the inner parts of the fruit into distinct segments, leaving hollow areas at harvest maturity.  Hollow heart occurs more often in the first-formed fruit on the plant, as a result of excess nitrogen fertilization and delayed harvests.  The disorder is more prevalent under conditions of rapid fruit growth rate, when the rind is expanding more rapidly than the inner regions of the fruit.  Ways of avoiding the condition include selection of less susceptible cultivars, and using cultural practices that moderate fruit growth rate and final fruit size.  These include adequate plant populations, moderate levels of nitrogen, and prompt harvests.” 

 

 

 

Sandea Can Carryover to Some Vegetables - Mark VanGessel, Extension Weed Specialist;  mjv@udel.edu

 

Sandea is labeled for use in a number of vegetable and melon crops.  However, it is not safe for all vegetables and this includes vegetables planted in rotation with crops treated with Sandea (halosulfuron).  Last year a few fields were planted with pickles, treated with Sandea, and rotated to spinach.  The spinach crop was injured due to halosulfuron carryover.  So check your herbicide labels to be sure there are no problems with herbicide carryover.

 

 

 

Field Crops

 

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

Alfalfa.
Continue to sample all fields on a weekly basis for leafhopper adults and nymphs. Once fields are yellow, stand and yield loss has already occurred. We are starting to see a significant increase in nymphs which often cause damage very quickly. The treatment thresholds are 20 per 100 sweeps on alfalfa 3 inches or less in height, 50 per 100 sweeps in 4-6 inch tall alfalfa and 100 per 100 sweeps in 7-11 inch tall alfalfa. Baythroid, dimethoate, Mustang or Warrior will provide effective control. Early cutting is also a control option, but be sure to check fields within a week of cutting for leafhoppers.

 

Field Corn
Continue to scout corn for grasshoppers feeding on small plants. A grasshopper treatment should be considered if you find 5-8 grasshoppers per square yard. Asana, Dimethoate, Lorsban, Furadan and Warrior will provide control but multiple applications may be needed.

 

Continue to scout whorl stage corn for European corn borer. Corn borer control will not be needed until 50% of the planted are infested in irrigated fields and 80% of the plants are infested in dry land fields. Since corn is growing quickly, the best time for control will be just at pre-tassel or tassel emergence as long as larvae have not bored into the midribs of leaves.

Soybeans.
Grasshopper and bean leaf beetle feeding continue to be found in seedling stage soybean fields. A treatment for bean leaf beetle will be needed from plant emergence to the second trifoliate when you find 2 beetles per ft. of row and a 25% stand reduction. A pyrethroid, dimethoate or Lorsban will provide control. The treatment threshold for grasshoppers is 1 per sweep and 30% defoliation. Asana, Furadan, Lorsban, or Warrior will provide grasshopper control.  We are starting to see a significant increase in the number of thrips in soybean. However, no treatment is needed until you find 8 thrips per leaflet, and plant growth is being held back.

 

 

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

 

Small Grain.

Barley harvest is underway and from a disease perspective small grain diseases have been relatively minor compared to last year. A few scattered fields in the northern part of the state have had some head blight or scab (estimate at less than 1 percent) and some tan spot. At this point rust is showing up now on any wheat that is late, but will not affect yield. The major problem downstate appeared to be drought damage especially on sandy knolls. Some fields have sooty mold where the drought damaged plants died prematurely and these black fungi grow saphrophytically on the heads.

Field Corn.

Anthracnose leaf blight is showing up in scattered areas on corn following corn and corn fodder is present. There are large differences in susceptibility among hybrids as you can imagine. Usually seedling infections or infection of young plants is not important and the corn often grows out of it. If the hybrid is susceptible and favorable weather for infection occurs later in the season, the spores from the early infection can infect the leaves and/or stalks and cause problems later. Anthracnose stalk rot is very common throughout Delaware, especially when corn borer damage is present. Leaf symptoms can vary depending on the hybrid, environment and age of the leaf, but generally look for 1-2 inch long elliptical spots with tan centers and red, reddish-brown or yellow borders. With a 10X hand lens you can often see the small hair-like structures called setae rise above the spots, which is a positive diagnostic feature for anthracnose.

 

 

 

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