Volume 6, Issue 15                                                                                             July 3, 1998


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

Lima Beans.

As soon as the earliest planted fields begin to flower and set pods, fields should be sampled for lygus bugs and stink bugs. Populations of both of these insects have already started to increase in the earliest planted fields. Treatment should be considered if you find 15 adults and/or nymphs per 50 sweeps. Lancet should be used if both species are present.


Continue to watch for increases in melon aphid and mite activity. Although aphid populations have increased, beneficial insect activity appears to be taking care of aphid populations. If you have sprayed for mites and need a second application, it is important to consider using an insecticide with a different mode of action to reduce the chances of developing insecticide resistance. In our experiences this season, dimethoate has given poor to fair control. Kelthane on the other hand has provided control for at least 2 weeks. Agri-Mek should also be considered for mite control. Be sure to add a sticker similar to Plex if Agri-Mek is applied by air.


In areas where corn borer catches are above 2- 3 per night, peppers should be sprayed on a 7 – 10 day schedule. If Orthene is used, a 10-day schedule will be adequate and it will also provide pepper maggot control. If a pyrethroid or Lannate is used, sprays should be applied on a 7-day schedule and dimethoate should be added to the mix for pepper maggot control.


We are starting to see an increase in Colorado potato beetle adult activity as well as an increase in egg laying and hatching. If the predominant life stage is small and large larvae, Kryocide/Cryolite or Agri-Mek should be used. Once you see a significant increase in adult activity (50 per 100 plants), then Provado should be used. Aphid activity has also increased in the earliest planted fields where Admire was not used at planting. Within the 2 weeks before harvest, the treatment threshold is 10 per leaf. Monitor or Provado will provide green peach aphid control. Lannate or Provado will provide melon aphid control.

Snap Beans.

All processing snap beans should be sprayed at the bud and pin stages for corn borer control. Orthene should be used at a rate of 1 1/3 lb per acre for corn borer control. If corn borer catches remain above 2-5 per night after the pin spray, a treatment with Lannate will be needed within 5-7 days from harvest. Starting at the pin stage, fresh market snap beans should be sprayed on a 7-day schedule with Lannate for corn borer control.

Sweet Corn.

All fresh market silking sweet corn throughout the state should be sprayed on a 3-4 day schedule. *


Vegetable Diseases - Bob Mulrooney, Extension Plant Patholgist ; bobmul@udel.edu


Quadris (Zeneca Ag Products) and Nova 40W (Rohm and Haas) fungicides for use on cucurbits was granted a crisis exemption as of July 1, 1998 by the Delaware Dept.of Agriculture. As mentioned by Kate Everts last week, the section 18 application for these products to control powdery mildew was submitted in early March. Because of staffing problems the agency was not able to process the request before powdery mildew appeared on the shore. For powdery mildew control we are recommending that growers (add) start

with two sprays of Nova (48 hr PHI) plus their protectant (Bravo, etc.) when the disease is detected (one lesion found on the underside of 45 old leaves). Follow the Nova applications with two sequential applications of Quadris. Quadris has a shorter PHI (24 hrs) which makes it very useful during harvest, and will also control gummy stem blight It is important that Nova and Quadris are not applied more than twice sequentially. We are recommending that the first Quadris spray be the 11.5 fl. oz. Rate followed by a 15.4 fl. oz rate. This is to prevent resistance from developing and the reason why we wanted two products with different chemistry to prevent resistant strains of powdery mildew from developing.

Snap and Lima Beans.

To prevent damping-off and seedling rot caused by Pythium and Rhizoctonia apply Ridomil PC 11G in the seed furrow at planting. These diseases are more prevalent in the second crop where beans follow peas or snapbeans, and when plantings are made during wet, hot, and humid conditions.

Late Blight Update

DSV accumulations as of June 29, 1998 are as follows:

Location/Emergence Date

DSV's June 25

DSV's June 29


Baldwin - 4/20



5-day, mid rate

Jackewicz - 4/20



5-day, mid rate

Zimmerman - 4/23



10-day, mid rate

Baker - 5/1



5-day, mid rate

We are still accumulating DSV's so protective spraying should continue as long as there is green foliage to protect. Late blight has occurred all around us except for New Jersey. Keep up the good work.

We recently diagnosed early dying in a field used for plot work and confirmed the presence of Verticillium in the stems and very high lesion nematode counts in the roots (2,460 and 3,684 per 10 grams of roots). This illustrates what I mentioned before that diagnosis should include roots as well as infected stems. Fields that have been rotated three years or more or are new to potatoes that exhibit early dying symptoms should be sampled to confirm the presence of either or both pathogens.

New Jersey reported that late blight was detected on Long Island on June 22. This was 10 days after a period of 5-7 inches of rain. The field was 50% defoliated by blight. Heavily infected areas were vine killed and the rest of the field was sprayed with Tattoo C.

The Late Blight Report is also posted electronically at the UD Extension IPM website: http://www.udel.edu/IPM *


Vegetable Diseases - Kate Everts, Extension Plant Pathologist, University of Maryland and University of Delaware ; everts@udel.edu

MELCAST for Fungicide Application on Watermelons.

Do not use MELCAST if there is a disease outbreak in your field, it is a preventative program. Below are the EFI values from weather stations located on the Eastern Shore June 24 - July 1. Any questions please call Phil Shields at (410) 742-8788 or e-mail: ps136@umail.umd.edu

EFI Values



















Wootten Farms, Galestown,MD









Mark Collins, Laurel, DE









U of D, REC Georgetown, DE









Vincent Farms Laurel, DE









Watermelon Fields should be sprayed with a fungicide when 30 EFI values have been accumulated by the weather station nearest your fields. Add 2 points for every overhead irrigation. After a fungicide spray, reset your counter to 0 and start over. If a spray has NOT been applied in 14 days, apply a fungicide and reset the counter to zero. The first and last day above can be partial days so use the larger EFI value of this report and other reports for any specific day. *

Field Crops

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


Grasshopper problems have increased during the last week, especially in sorghum; along edges of field corn fields; and in soybeans planted into wheat stubble. As a general guideline, non-crop areas should be treated if you find 20 or more grasshoppers per square yard. In corn and sorghum, a treatment is justified if you find 5-8 grasshoppers per square yard. In soybeans, the threshold is one per sweep and 30 percent defoliation. Sevin and Warrior are labeled on all three crops and have provided the most consistent control. Dimethoate is labeled but must be applied when grasshoppers are small to get effective control. *


Grain Marketing Highlights - Carl German, Extension Crops Marketing Specialist ; clgerman@udel.edu

NASS Releases June 30, 1998 Grain Stocks and Acreage Reports

Corn Stocks Up 22 Percent

U.S. corn stocks in all positions on June 1, 1998 totaled 3.04 billion bushels, 22 percent above a year earlier. Of the total, 1.83 billion bushels are stored on farms with 1.21 billion bushels stored in off-farm facilities. Disappearance of corn stocks from March to May was 5 percent below the disappearance during the same time last year.

Wheat Stocks Up 67 Percent

All U.S. old crop wheat stored in all positions June 1, 1998 totaled 723 million bushels, up 63 percent from June 1, 1997. On farm stocks represented 224 million bushels of the total with off-farm stocks placed at 499 million bushels. The disappearance for wheat for the fourth quarter was 443 million bushels, up 17 percent from the same period in 1997.

Soybean Stocks Up 19 Percent

U.S. soybeans stored in all positions on June 1, 1998 totaled 593 million bushels, up 19 percent from last year. On farm stocks totaled 318 million bushels with off-farm stocks reported at 275 million bushels. Indicated disappearance for the March-May period totaled 610 million bushels, 10 percent above the same period last year.

Corn Acreage Up 1 Percent

Soybean Acreage Up 3 Percent

Corn planted for all purposes is estimated at 80.8 million acres, up 1 percent from last year. This represents the largest planted acreage since 1985. Corn expected to be harvested for grain this fall is estimated at 74.3 million acres, the largest harvested acreage since 1985. Excellent weather in the corn belt helped planting to finish 1 week ahead of the normal pace. Soybean acreage is estimated at 72.7 million acres, 3 percent above last year's crop. Area for harvest is estimated at 71.7 million acres. If realized, this will be the largest planted and harvested acreage on record. The last record was set in 1979.

"Rain Makes Grain" as Commodity Prices Fall

Commodity prices at the Chicago Board of Trade pulled back this week as conditions for crop development in the Midwest have turned more favorable, from the previous week. One only needs to check the calendar to figure that pricing opportunities, due to changes in weather conditions, are very likely to be forthcoming. *


Are Deer Reducing Your Forage Yields? Richard W. Taylor, Extension Agronomist ; rtaylor@udel.edu

Recently, Drs. Marvin Hall and R. Stout from the Pennsylvania State University reported on a study to evaluate deer damage on forage crops. Deer damage on alfalfa can be substantial and impacts yield, stand survivability, and rate of weed invasion. They found that forage crops (alfalfa, orchardgrass, timothy, and combinations of alfalfa and the two grasses) protected from deer feeding averaged 1660 lb/A more dry matter (DM) yield than their unprotected counterparts. Total yield reduction ranged from 435 lb/A for pure stands of orchardgrass to 1,230 lb/A for pure stands of timothy to 2,392 lb/A for pure alfalfa stands. Deer feeding resulted in average economic losses of $80/A for pure alfalfa and $28/A for pure orchardgrass. Weed density increased more in the unprotected than in the protected plots of each species or combination of species.

In the study, they planted three different mixture ratios of alfalfa and each grass. Deer grazed alfalfa selectively from alfalfa-grass mixtures and fed on plots containing timothy more than those containing orchardgrass. Averaged across all mixtures, alfalfa composed 35 percent of the total yield in the protected plots but only 19 percent in the unprotected mixed plots. For the alfalfa-grass mixtures, average yield reductions, as a result of deer feeding, were 1,507 and 1,102 lb/A for treatments containing timothy and orchardgrass, respectively. These values did not include weed yield from these plots in the second year of the study. This research indicated that the greatest economic loss from deer is for pure alfalfa stands, followed by alfalfa-timothy combinations, and then by alfalfa-orchardgrass mixtures.

What implications did their study have for forage producers? In areas that experience significant deer feeding, pure orchardgrass and alfalfa-orchardgrass mixtures are the best choices. Pure orchardgrass also had the least weed infestation in the second year. Because of improved forage quality, the greatest economic returns were for alfalfa-orchardgrass mixtures but only when alfalfa was seeded at 50 percent or more of the mixture.

The study did not look at several other species such as tall fescue; reed canarygrass (low alkaloid varieties); perennial or tetraploid ryegrass; and, in the northern portions of the area, Kentucky bluegrass and smooth bromegrass. However, I would suspect that tall fescue and reed canary grass would be similar in response to orchardgrass and that the other species would have responses similar to timothy. *


Weed Control in Those Drowned Out Areas - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

Many wheat fields have areas where the wheat was drowned out due to spring rains and there is heavy weed pressure in these areas. These areas should be sprayed with Roundup Ultra or Touchdown to control the weeds. Since many of these areas have lots of large grasses in them, Gramoxone Extra is not a good choice. Minimum use rates should be Roundup Ultra at 1.5 qts/A or Touchdown at 1.0 qt/A. For best results, apply Roundup Ultra or Touchdown alone rather than as a tank-mixture, but this may require an additional application. Due to the size of some of the weeds an in-crop treatment maybe necessary, particularly if the combine header cut off a large portion of the weed. *


Crop Injury versus Weed Control - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

Soybeans can tolerate injury from postemergence herbicides with no yield loss. The way the soybeans look right after application is often not a good indicator of yield loss. Leaf discoloration and slight leaf burn (leaf burn but leaves do not drop off) seldom translate into yield loss. Many factors go into determining the yield, with moisture at flowering being the most critical. Leaf speckling is often superficial and within 10 days it is difficult to see the effect. However, herbicides that cause soybeans to drop their leaves right after application can affect yields. Select the herbicide based on its weed control performance. Avoid additives that can increase crop injury. For instance, additional nitrogen can increase injury and crop oils cause more injury than non-ionic surfactants. When given the choice of more than one option for herbicides and surfactants, first consider if the herbicide will control the weeds you have. A herbicide that has no effect on the soybean leaves, but does not control the weeds is not the right choice. *


Soybean Twilight Tour - Mark VanGessel, Extension Weed Specialist ; mjv@udel.edu

A tour of the soybean plots at the University of Delaware’s Research and Education Center in Georgetown will be held on July 22 beginning at 6:30 p.m. The Research and Education Center is located on Route 9 midway between Highways 13 and 113. Soybean varieties, weed control, and current research on production practices will be highlighted. The tour is open to everyone. Refreshments will be provided. Contact Mark VanGessel, 302/856-7303, if you have any questions. *

Weather Summary

Week of June 26 to July 2

0.40 inches: June 27
Readings taken for the previous 24 hours at 8 a.m.
Air Temperature:
Highs Ranged from 95 F on June 27 to 76 F on June 29.
Lows Ranged from 82 F on June 27 to 56 F on June 29.
Soil Temperature:
74 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

Extension Associate - Vegetable Crops

Cooperative Extension Education in Agriculture and home Economics, University of Delaware, Delaware State College and the United States Department of Agriculture cooperating, John C. Nye, Dean and Director. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. 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.

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