Volume
10, Issue 15
July 5, 2002
Volume
10, Issue 15
July 5, 2002
Vegetables
Vegetable Insects
-
Cucumbers.
With the continued hot, dry weather, continue to watch both pickles and slicers for increases in aphid populations. A treatment should be applied for aphids if 10 to 20 percent of the plants are infested with aphids. Actara, Fulfill, Thiodan or Lannate will provide control. Be sure to watch for bees foraging in the area and avoid insecticide applications on blooming crops.
Lima
Beans.
Continue to 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 Mustang can be used if both species are present.
Potatoes.
Aphid populations have started to increase in later planted fields. A treatment should be considered if you can find 4 aphids per leaf. Remember, green peach aphids are generally found on the underside of the lowest leaves, so be sure to sample the correct area of the plant. Actara, Fulfill or Provado will provide green peach aphid control. We have had reports of growers describing significant levels of corn borer damage. Upon examination of fields, most of the damage has not been caused by corn borer. Although low levels of corn borer stem infestations are present, the greatest damage has resulted from bacteria splashing into the leaf petioles ("aerial stem rot"). This often occurs when growing conditions are dry, fields are constantly irrigated and windy conditions persist. No controls are available for this "aerial stem rot".
Melons.
Economic levels of spider mites, thrips and aphids can still be found in melon fields. A treatment will be needed if you find 20-30% of the plants infested with 1-2 mites per leaf. Agri-Mek, Kelthane and Capture have provided effective control this season. Be sure to watch for an increase in aphid populations. A treatment is needed if 20% of the plants are infested with 5 or more aphids per leaf. High numbers of thrips can still be found in later planted melons. No thresholds are available, but a control may be needed if plants are stressed and populations continue to increase. A pyrethroid or dimethoate should help to reduce populations.
Peppers.
Corn borer controls are needed in areas where pepper fruit is ½ inch in size or larger. If acephate (Address/Orthene) is not being used, then dimethoate should be added to the mix for pepper maggot control.
Snap
Beans.
Fresh market and processing snap beans in the bud to pin stage will need to be sprayed for corn borer control. Seedling beans should still be watched for thrips and leafhopper activity. If both insects are present, the threshold for each should be reduced by 1/3. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. We have started to find defoliators feeding on the pin pods. Even though corn borer counts remain low, a treatment should be applied if defoliators are feeding on pin pods. Lannate, Asana, Capture or Mustang will provide the best control of defoliators.
Sweet
Corn.
Fresh market silking sweet corn
should be sprayed on a 4-5 day schedule. Be sure to make the first application
when ear shanks are first visible. The first fall armyworm has been found in
whorl stage corn, so be sure to sample all late planted fields for fall
armyworm larvae. No controls will be needed until 15% of the plants are infested.
Diagnosing
Nutritional Disorders -Ed Kee,
Extension Vegetable Crops Specialist; kee@udel.edu
When confronted with diagnosing a possible deficiency in plant nutrients, it is helpful to remember which elements are immobile in the plant and which are mobile. The deficiency symptoms of immobile elements appear on the young tissue, because they are not easily translocated from older leaves to newer leaves. Iron and manganese are the two elements that will appear as a deficiency on new and recently maturing leaves.
Nitrogen, Phosphorus, Magnesium, and Potassium will exhibit deficiency symptoms on mature leaves, because these elements move readily to active tissue sites such as young leaves. Each element will have specific symptoms, but the location of the symptoms brings into focus the possibilities.
Perhaps the most common deficiency occurs with nitrogen, usually due to leaching or some factor that has limited nitrogen application. It is a general light green or yellow-green chlorosis of the entire leaf tissue beginning on mature leaves, but over extended periods will involve the new growth. Growth is eventually retarded, but is easily corrected with the application of nitrogen. If it has gotten that severe, yield and quality of vegetables will be negatively affected.
Vegetable Diseases
-
Ozone
and Watermelons.
Current weather conditions have resulted in high ozone levels. Ozone injury, chlorosis and scorching of the upper leaf surfaces, is present in watermelons. Damage is most prevalent in older, crown leaves. Little can be done to protect the current crop. To reduce ozone damage on future crops, plant cultivars that are ozone tolerant such as Millionaire, Millennium, or Tri-X-313. Avoid cultivars that are sensitive to ozone such as Sugar Baby, Crimson Sweet or Fiesta. See the Commercial Vegetable Production Recommendations 2002 for more information on cultivar sensitivity or tolerance.
Fusarium Wilt.
Fusarium wilt in watermelon is present in several fields on Delmarva. Symptoms often appear when the vines produce runners and become more severe as fruit are increasing in size. Symptomatic plants appear water-stressed when soil moisture is adequate. Crown leaves wilt first, followed by runners and eventually the whole plant. Infected stems may have a red, brown or black gummy exudates and the vascular system of the plant is discolored.
Management of Fusarium wilt has
been accomplished in the past through long rotation (5 to 6 years), planting
resistant cultivars and fumigation.
However, fumigation may fail to control disease because Fusarium can quickly reinvade fumigated ground. A new aggressive form of the pathogen (Fusarium oxysporum
f. sp niveum, race 2) has been detected in
From the
Latest EFI values from local weather stations
Any
questions please call (410) 742-8788
EFI Values (Environmental Favorability Index)
Do
not use MELCAST if there is a disease outbreak in your field, it is a preventative program.
Location
Charles Co. 1 0 0 0 8 7 3
Collins Farms 2 1 2 2 3 2 0
Vincent Farms 3 3 2 3 4 3 0
White Marsh 0 0 0 2 1 7 0
The first fungicide spray should be applied when the watermelon
vines meet within the row. Additional
sprays
should be
applied using MELCAST. Accumulate EFI
(environmental favorability index) values beginning the
day after
your first fungicide spray. Apply a
fungicide spray when 30 EFI values have 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 0 and start over. The first and last
day listed above can be partial days so use the larger EFI value
of this
report and other reports for any specific day.
If, for some reason, a serious disease outbreak occurs in your field, return to a weekly spray schedule
More
detailed information concerning MELCAST and sample data sheets are available on
the web at http://www.agnr.umd.edu/users/vegdisease/vegdisease.htm.
Vegetable Diseases
-
Potato Disease Advisory.
Late
blight Advisory
Disease Severity
Value (DSV) Accumulations as of
|
Date |
Total DSV |
Spray
Recommendation |
|
5/1 |
12 |
None |
|
5/11 |
19 |
5 days, low rate |
|
5/19 |
23 |
10 days, low rate |
|
5/22 |
23 |
10 days low rate |
|
5/27 |
27 |
10 days low rate |
|
5/29 |
30 |
7 days, low rate |
|
6/3 |
33 |
7 days, mid-rate |
|
6/5 |
33 |
10 days, mid-rate |
|
6/9 |
38 |
7 days, high-rate |
|
6/13 |
39 |
10 days, high-rate |
|
6/16 |
58 |
5 day mid- rate |
|
6/19 |
60 |
10 day mid-rate |
|
6/23 |
63 |
7 day high rate |
|
6/26 |
64 |
10 day high rate |
|
6/30 |
66 |
10 day high rate |
All potatoes have reached more than 18 DSV’s. The Wisdom potato software program generates spray recommendations.
Late blight has not been a problem here in
NOTE: For this greenrow date and location we have accumulated 590 P-days as well. P-days are a measure of potato plant growth somewhat similar to growing-degree-days. When 400 P-days have been exceeded, conditions for early blight infection are more favorable and disease may begin to show up 5-7 days later. Continue fungicide sprays for early blight.
Late blight has not gone away completely. There was a recent
report this week of late blight in
Note: This will be
the only advisory this week. The potato crop looks great.
Field Crop Insects
-
Alfalfa.
In addition to leafhoppers, be sure to watch for defoliators in alfalfa. A number of defoliators are present in alfalfa including green cloverworms, salt marsh caterpillars and alfalfa caterpillars. If you have reached 1/2 the leafhopper threshold and you are approaching 50% tip damage from defoliators, a treatment should be considered.
Field
Corn.
We can now find Japanese beetles and corn rootworm adult beetles feeding on silking corn. The decision to treat should be based on the number of beetles per ear as well as how far you are in the pollination period. As a general rule, a treatment is recommended on silking corn if you can find 4-5 Japanese and/or corn rootworm beetles per plant and they are clipping silks to less than ½ inch long before 50% pollination.
Soybeans.
Continue to watch for spider mites, leafhoppers, grasshoppers and defoliators in soybeans. We are starting to see an increase in spider mite and leafhopper populations. A treatment for leafhoppers is not recommended unless you find at least 4 per sweep in drought-stressed beans or 8 leafhoppers per sweep in actively growing soybeans. The treatment threshold for spider mites is 20-30 mites per leaflet or 10% of plants with 1/3 or more leaf area damaged. Dimethoate, Lorsban and Parathion (aerial application only) are the only available options so early detection and control will be critical. If dimethoate is used, the addition of a penetrant like LI-700 or AD 100 has been shown to improve the performance. Japanese beetle adults and feeding damage has increased in full season soybeans. No controls will be needed pre-bloom unless you find 7 beetles per foot of row and 30% defoliation. If plants are blooming, the threshold decreases to 15 % defoliation. If a combination of insects is present, the threshold for each pest should be reduced by one-third.
Yellow Soybeans
with Roundup-Ready Soybeans - Mark VanGessel,
Extension Weed Specialist;
mjv@udel.edu
Last year it was not uncommon to see yellowing or even whitening in the growing points of soybeans after spraying glyphosate on Roundup-Ready soybeans. The symptoms may take up to two weeks to develop. Excessive heat and drought conditions seem to increase the severity of the symptoms. This year it seems to be more dramatic and more widespread than in past years. It seems to be the same for all glyphosate formulations. It is worse where there were overlaps or in the turn rows. The beans will grow out of the symptoms. Based on last year’s experience, the yellowing does not affect the height of the beans or vigor.
UPCOMING
EVENTS:
AGRONOMIC CROPS
TWILIGHT SESSION
Location:
University
of Delaware Cooperative Extension invites you to join your fellow farmers and other members
of the agricultural community as our Extension Specialists lead
discussions of this year’s field trials and other in-season
issues related to corn, soybeans, and small grains. Other
topics will include both grain marketing and farm bill
highlights. We expect to have the 2001-2002 wheat and barley
variety trial results for distribution and discussion. There will be time to discuss your
current cropping issues.
We will
wrap-up the evening with an award presentation and ice
cream treat!
CREDIT toward
The meeting
is free and everyone interested in attending is welcome. For more information or for special
consideration in accessing this meeting, please contact us at 831-2506.
HOPE
TO SEE YOU THERE!
Carl P.
Davis
Extension Agent, Agriculture
Week of June 27
to
|
|
Rainfall: 0.28 Inches on June 27th |
|
|
|
Air Temperature: |
|
Highs
Ranged from 94°F on July 2 to 83°F on June 28. |
|
Lows
Ranged from 72°F on June 27 to 62°F on June 30 & July 1. |
|
Soil Temperature: |
|
83°F
average for the week. |
|
(Soil
temperature taken at a 2 inch depth, under sod) |
Web Address for the U of D
Compiled and Edited By:
Tracy Wootten
Extension
Associate - Vegetable Crops
Have a Happy and
Safe July 4th !
Cooperative
Extension Education in Agriculture and Home Economics, University of Delaware,
Delaware State University and the United States Department of Agriculture
cooperating, Robin Morgan, Dean and Director.
Distributed in furtherance of the Acts of Congress of
May 8 and