Weekly Crop Update

University of Delaware Cooperative Extension

Volume 5, Issue 18

July 31, 1997





Watermelon Twilight Meeting

August 5, 1997

5:30 p.m. - Until?

Located on Route 24 at Mark Collin’s Farm, Near Laurel Airport.


View the commercial size research plots for a weather based fungicide application model for the control of gummystem blight and anthracnose in watermelon.


( The plots sprayed according to the model have saved 2 fungicide sprays compared to the weekly fungicide sprays. At this writing, no differences in disease control has been found)


New varieties from the Uof D’s seedless watermelon and large seeded watermelon variety trials will be on hand.


An update on mite and melon aphid control.


Agents and Specialists will be available to answer any questions you may have concerning production this year.

 Meeting begins at 5:30 p.m. with dinner to follow.

 For more information, contact Charlotte Headley at 302-856-7303.


Field Crops:

Field Crop Insects -

Joanne Whalen, Extension IPM Specialist.




Mite populations are still at economic levels throughout the state. In most cases, weather conditions at the end of last week did not help to crash populations. In areas that received rain, dimethoate should provide good control, especially if applied in at least 20 gallons of water per acre. In a mite control trial sprayed last Friday at the Research and Education Center, we got excellent control with dimethoate and a few experimental compounds applied in 20 gallons of water per acre. We also tried Warrior at 3.84 oz per acre. Although it reduced populations, the level of control would only be considered suppression. In areas where dimethoate alone or dimethoate plus Penncap/Parathion have not provided control, a combination of dimethoate plus Warrior should be considered. It is also time to sample the earliest planted fields for corn earworm. Although we do not expect significant corn earworm populations in soybeans, we are starting to see an increase in moth activity in blacklight and pheromone traps. Begin sampling fields as soon as small pods are present. The treatment threshold is 3 per 25 sweeps in narrow row beans and 5 per 25 sweeps in wide row beans. Ambush, Asana, Larvin, Pounce or Warrior will provide control.


Fertigating Corn -

Richard W. Taylor, Extension Agronomist



In corn, potash (K) uptake is essentially complete soon after silking (R1 growth stage) while nitrogen (N) and phosphorus (P) uptake in corn continues until near maturity. However, by the blister (R2) stage nearly 80 percent of the total N needed by the crop has been accumulated. Later in the season during grain fill, both N and P are translocated from vegetative plant parts (leaves and lower stalk) to the developing grain. This translocation can lead to nutrient deficiencies in the lower leaves unless adequate soil N and P are available to the plant during that period. Development of deficiency symptoms on the lowest leaves does not lead to a significant reduction in grain yield but, if symptoms proceed up the plant to the leaves below the ear, yield can be reduced.

 The critical period for nutrient uptake is early in the season when the final size of the leaves, ear, and other plant parts is determined greatly by the availability of an adequate supply of nutrients (especially N). Although fertigation permits many small applications of N fertilizer, significant N should be applied early during crop growth. In general, the best approach is to apply all the required N as estimated using realistic yield goals by the blister (R2) growth stage. Corn will store extra N in the lower leaves and lower stalk where it can be mobilized during grain fill. A hybrid will mature normally and produce grain most efficiently when nutrient translocation ( reallocation from other plant parts) occurs, but where it is not so excessive that it results in premature death of leaves and consequently a reduced rate of grain formation.

This approach is ideal for the following reasons:

Early N is necessary to ensure maximum leaf area, ear size, and maximum yield potential

Corn can store extra N in the leaves and lower stalk for later mobilization to the developing kernel and this mobilization is needed for efficient grain production.

Spoon feeding throughout the season (versus all applied at planting or all applied at planting and sidedress time) reduces the chance that too much N will be leached out of the root zone by heavy rains or loss through denitrification

Heavy rainfall after blister stage could seriously delay additional N applications resulting in reduced yields if only enough N is applied at each growth stage to maintain growth (none has accumulated in the leaves or lower stalk)

Excess N does not remain in the soil but rather is taken up from R2 to maturity


Who You Going to Call? Ghostbusters?

Richard W. Taylor, Extension Agronomist



I know many of you are concerned with how much damage the drought has done to your corn fields and, as a result of that concern, you'll be out walking your fields to get a sense of how much damage was done. If you do, don't be surprised to see a slimy film or even a gelatinous mass near the base of the stalks where brace roots emerge. You won't have to call the ghostbusters. It is a natural process in which the corn produces a mucilaginous material that lubricates the brace roots to make penetrating the soil easier. It also protects the roots from damage during entry.

 So what good are brace roots? Brace roots or aerial nodal roots not only help support the plant as the ear fills but also scavenge the upper soil layers for water and nutrients during reproductive growth stages.

 If you're trying to evaluate whether the drought hurt pollination, try this. When the silks are mostly brown and pollen shed has stopped, sample a few random ears across your field. Carefully remove the husks and then shake the ear to allow loose silks to fall away from the newly forming kernels. Any silks that remain attached to the ear indicate an unfertilized ovule (potential kernel). Mostly, these will be near the tip of the ear. In this way, you can estimate how much of the ear was fertilized and by carefully sampling across a field you can estimate in a very rough way the approximate yield loss from past drought and heat stress.


Grain Marketing Highlights -

Carl German, Extension Specialist, Crops Marketing



The grain markets appear to be in a quandary right now in terms of determining price direction. The key to the markets may well be the August crop report, when crop size for 1997 U.S. corn and soybean production begins to get more definitive. As of July 29, 1997 the new crop corn and soybean futures contracts are trading in a mid-point range when compared to the season high and low for the contracts, $2.60 for December corn and $6.37 for new crop soybeans. Market analysts have indicated that rains will turn prices south, while continuance of dry weather will likely drive prices higher. With the extreme dry conditions locally, it is better to discuss possible marketing strategies on an individual basis. For further information contact Carl German @ 831-1317.


Vegetable Crops:

Vegetable Crop Insects -

Joanne Whalen, Extension IPM Specialist.




It is time to start checking ferns for asparagus beetle adults and larvae. An August application of an insecticide has helped to reduce spring populations and egg laying on spears. Ambush, Pounce, or Sevin will provide control.



Corn borer moth catches have started to increase, especially in the Harrington area where trap catches have reached 20 per night. In the Harrington area, corn borer sprays should be applied on a 5 day (Lannate or pyrethroid) to 7 day schedule (Orthene). In all other areas, sprays should be applied on a 7 day (Lannate or pyrethroid) to 10 day schedule (Orthene). Continue to watch for aphid explosions if a pyrethroid is used on a routine basis. Once corn earworm blacklight trap catches increase to 20 per night, Lannate will be the preferred material.


Pickling Cucumbers.

Along with pickleworm, be sure to watch for an increase in melon aphid populations. High levels can now be found in isolated sections of fields. Remember, Lannate is the only labeled material available on pickles that will provide melon aphid control.


Snap Beans.

With the increase in corn borer moth activity, fresh market snap beans should be sprayed on a weekly basis from the pin stage until harvest. Lannate is the material of choice. Processing snap beans should be sprayed at the bud and pin stage with Orthene. In the Harrington area, Asana should be combined with Orthene at the pin spray for corn earworm control. In most areas of the state, sprays are needed on a 6-7 day schedule after the pi spray. However, in the Harrington area, sprays are needed on a 4-5 day schedule after the pin spray.


Sweet Corn.

Fall armyworm populations are starting to increase in the latest planted fields. Populations are ranging from 20 to 35% infested fields. Warrior or Larvin have provided the best control. Fresh market silking sweet corn should be sprayed on a 3-4 day schedule.


U of D Crop Pest Hotline:

In State: 1-800-345-7544

Out-of-State: 302-831-8851


Basagran on Lima Beans and Related Weed Control Issues -

Ed Kee, Extension Vegetable Specialist



Basagran has been used successfully on lima beans to control broadleaf weeds that have escaped through the preemergence treatments and cultivation. The lower rate of 1 pint/acre will control common cocklebur, mustards, and jimsonweed and the higher rate will control common lambsquarters, ragweed, and Canada thistle. All of these weeds must be six inches or shorter to expect good control. Check your fields early. The lima beans must have at least one fully expanded set of trifoliate leaves. There are good experiences with Basagran killing larger jimsonweeds (6 to 12 inches), but this is with the higher rate and dependent on a lot of variables, including good spraying conditions. Applying Basagran when the weeds are smaller is critical to obtaining good control.

 Horsenettle is a troublesome weed in lima beans because the berries are hard to separate from the harvested beans at the factory. Although most processors have installed equipment especially designed to remove the berries at the factory, it is still very important to keep them out of the system if at all possible. Applications of Basagran can stunt and delay horsenettle growth to help keep berries from forming at harvest time. This application may be useful for large spots or populations of horsenettle.

 Little morningglory control should be expected from Basagran, unless the morningglories are very young.

 Crop oil concentrate should be used with Basagran, and while it may cause a temporary yellowing or burning, lima beans are tolerant and grow out of these symptons.

 Reflex is labeled for postemergence use in several states on green beans (snap or string beans). It is not labeled for lima beans. Unfortunately, lima beans are susceptible to injury from Reflex.


UpComing Events...









8:30 a.m. - 1:30 p.m.


Agronomic and Vegetable Field Tours

Wagons will depart from the area located behind

the pesticide storage and handling facility from 8:30 a.m. - Noon


  • Controlling Powdery Mildew on Cantaloupe - The Challenge of Resistance to Fungicides - Fungicides are a valuable tool in controlling vegetable and vine crop diseases. However, plant pathogen populations may shift in response to repeated exposure to a single fungicide. As resistant individuals become increasingly prominent, growers lose control options. A population shift has been observed in powdery mildew on cantaloupe. Tour participants will gain understanding of fungicide resistance in the dynamic pathogen population and the benefits of several alternative strategies in minimizing the development of resistance. Phil Shields, Faculty Research Assistant, Plant Pathology, University of Maryland; Dr. Kate Everts, Extension Plant Pathologist, Universities of Maryland and Delaware; Bob Mulrooney, Extension Specialist, Plant Pathology, University of Delaware


    Precision Agriculture: Technology of the Future? - Precision agriculture is a crop management system that uses satellite technology to identify precise locations in the field, map and record those locations, and then make crop applications of lime, fertilizer, herbicide or seeds in the exact amounts needed at precise locations in the field. These input applications are regulated by variable-rate controllers that "tell" the application equipment or sprayer how much to put out and where. Simply stated, Precision Agriculture Systems (PAS) rely heavily upon technologies that use electronics, satellites, and computers to do the right thing, in the right place, at the right time and in the right way. A variable-rate precision manure applicator will be highlighted as part of a demonstration of precision agriculture technology. Dr. Jim Glancey, Assistant Professor, Bioresources Engineering Department; Ed Kee, Extension Specialist, Vegetable Crops; Tracy Wootten, Extension Associate, Vegetable Crops


    High-Oil Corn: A Biotechnology Success - Biotechnology has enabled plant breeders to develop corn hybrids that produce grain with nearly double the usual amount of oil. The higher oil content concentrates more energy into this popular feed grain. This tour stop will feature one of several studies evaluating the agronomics of high-oil corn. One study evaluates the hybrid tolerance to post-emergence herbicides. A second study evaluates four top-cross hybrids--two using a six percent (oil) male pollinator and two using a seven percent male pollinator--at three plant populations. The top-cross technology will be discussed as will the cultural requirements for the crop. Also covered will be handling, storage, and testing needs. Dr. Richard Taylor, Extension Specialist, Agronomy; Bob Uniatowski, Extension Associate, Agronomy


    The Connection Between Weed Biology and Weed Control - Understanding the connection between the biology and ecology of weeds is a critical step to developing an efficient and sustainable weed management system. A number of research projects are being conducted examining aspects of weed biology and using this information in weed control decisions. This information will have an impact not only on effectiveness of weed control but can lower weed control costs. Dr. Mark VanGessel, Assistant Professor/Extension Weed Specialist


    Cultivating the Web - The World Wide Web and Internet provide a wealth of information for the farmer. See demonstrations on valuable and useful web sites that relate to the agricultural community. Learn what equipment you need and how to connect to the Internet and access this resource. Dean Dey, Technology Specialist


  • Landscape Demonstrations

    Demonstrations conducted from 8:30 a.m. - Noon


    Weed Identification Area

    Challenge your skills in identifying common troublesome weeds found in field crops, gardens, and lawns from 8:30 a.m. - Noon



    Sussex Master Gardener Demonstrations

    Exhibits and seminars open from 8:30 a.m. - 1:30 p.m.


    4-H Farm Animal Display

    Located west of the grove area (near USDA) from 9:00 a.m. - Noon


    Sussex County Safe Kids’ Day Activities

    Located in tent west of the grove from 8:30 a.m. - Noon


    Luncheon Program

    12:00 Noon in the grove

     A fried chicken lunch will be followed by a brief program. Tickets will be available at the registration. (Tickets are limited so early purchase is recommended.)


    Other Events and Activities

    Many agricutural-related demonstrations and exhibits will be on display beginning at 8:30a.m. Carriage rides will also be available.


    For more information contact:

    Mark Isaacs or Jay Windsor

    University of Delaware

    Research and Education Center

    RD 6, Box 48

    Georgetown, Delaware 19947

    (302) 856-7303



    Late Blight Report.

    DSV accumulation as of July 24, 1997 are as follows:


    Location/ Emergence date


    DSV’s July 21


    DSV’s July 24



    Baldwin - 4/20



    7-day, high rate

    Jackewicz - 4/26



    7-day, high rate

    Zimmerman - 4/28



    7-day, high-rate

    Baker - 5/7 -5/9



    5-day, high-rate


    For those growers with potatoes that still need to be protected. The recent, wet weather has produced conditions more favorable for disease development. Remember that Dithane and other mancozeb fungicides have a 3 day pre-harvest interval in Delaware. In Maryland and New Jersey the pre-harvest interval is 14 days. Late blight information hotline number 1-888-831-SPUD.



    Weather Summary

    University of Delaware,



    Week of July 25 to July 31, 1997



    0.72 inches: July 25

    Readings taken for the previous 24 hours at 8 a.m.



    Ranged from 92 F on July 28 & 29 to 74 F on July 25.


    Ranged from 73 F on July 29 to 55 F on July 31.


    Soil Temperature:

    72.9 F. Average for the week.




     Complied & 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. It is the policy of the Delaware Cooperative Extension System that no person shall be subjected to discrimination on the grounds of race, color, sex, disability, age or national origin.


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