Volume
10, Issue 1
March 15, 2002
Volume
10, Issue 1
March 15, 2002
The Weekly
Schedule Begins –
Issue 1 of Weekly Crop Update is a sample of the type of
information you will receive each week with a subscription or access via the
Internet. This newsletter is designed to
provide subscribers with the latest information on disease and insect problems
as they are developing, weed control information, crop progress reports, and
other timely topics related to agronomic and vegetable crop production in
Fruit
Fruit Insects - Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Peaches.
A Section 18 Emergency Use request was again submitted to EPA in February for the use of Provado on stone fruit to control aphids that vector the Plum Pox Virus. We will let you know as soon as we get a response from EPA.
Vegetables
Agricultural Fact -
46% of
Pea Planting Has Begun – Ed Kee, Extension Vegetable Crops Specialist; kee@udel.edu
Pea planting on Delmarva began in late February and
subsequent plantings have occurred as weather and temperature allow. Approximately 275,000 acres of peas for
processing are grown in the
Vegetable Diseases
- Bob Mulrooney, Extension Plant
Pathologist, bobmul@udel.edu
Back to Basics: Root Rot
Control in Peas, Lima Beans, and Snap Beans.
Root rot diseases are widespread and often cause significant yield losses. These diseases usually appear every year to some degree depending on weather and soil conditions. Root rot diseases are most severe and damaging when we have cool, wet conditions early in the season, followed by dry periods or other stresses like herbicide or insect damage, other diseases, or fertility problems. Poor soil conditions such as poor soil drainage and soil structure, low organic matter, low fertility and compaction make root rots worse.
Symptoms of root rot damage include poor seedling emergence and establishment, damping-off, stunting and uneven growth, chlorosis, and lower yield. Decreased root size, discoloration and decay characterize damage from soilborne fungi such as Rhizoctonia, Pythium, Fusarium on beans and Aphanomyces, Rhizoctonia, and Fusarium on peas. Many times, more than one pathogen is present which makes visual diagnosis difficult.
Management of these diverse soil fungi is difficult if you only utilize one management option. Effective management will be possible if you use an integrated approach of using a combination of cultural, biological and/or chemical control with appropriate soil management practices.
It is known that almost all crop and soil management
practices have a direct or indirect impact on root disease incidence and
severity. The use of cover crops and green manures can reduce or increase root
rot. Cover crop grain rye was shown in
In summary, root rot can be reduced if you can follow these steps:
· Use high quality disease-free seed treated with the appropriate fungicide for the pathogens you are likely to encounter.
· Practice crop rotation.
· Utilize cover crops, green manures and compost whenever possible.
· Reduce compaction and improve soil tilth.
· Plant at the appropriate time, depth and density.
· Select the best-adapted and tolerant varieties, if available.
Adapted for
Vegetable Diseases - Kate Everts, Extension
Vegetable Pathologist, University of
Pickling
Cucumbers.
Phytophthora fruit rot is a disease that can infect all cucurbit fruit including pickling cucumbers. Fruit rot is a different phase of crown and root rot, all caused by Phytophthora capsici. The symptoms of fruit rot are large water soaked lesions, which develop a white dense growth on the fruit. The disease can spread rapidly, causing fruit collapse during the growing season and after harvest. Like the crown and root rot phase, high soil moisture (typically standing water) for two days allows the sporangia to form and release zoospores. Secondary infections then occur. Heavy rain events, such as those resulting from hurricanes, may lead to complete crop loss. High disease levels can also occur in fall pickles that follow a spring crop that was under standing water.
Growers that have suffered losses due to this disease should plan ahead to minimize damage. Water management is critical to reducing damage from Phytophthora fruit rot. Select fields that have excellent drainage and avoid planting susceptible crops in low-lying areas where standing water is common. Plant on raised beds and subsoil (or “V-rip”) before planting to avoid soil layers that are impervious to water. A three-year rotation is important. Crops to avoid in the rotation are: cucurbits (including melon, watermelon, squash and pumpkin), pepper, tomato and eggplant. Broadcast soil fumigation can provide some benefit (for example, K-Pam and Telone list Phytophthora diseases on their labels). If fumigation is used, prevent nontreated soil from washing into the treated area.
Use of fungicides during the growing season is not always effective because of the presence of resistant strains of the fungus, difficulty obtaining adequate coverage and the aggressiveness of the disease when environmental conditions are favorable. However, Ridomil Gold Bravo applied when the vines begin to run, on a 14-day schedule may provide some disease control.
2002 Commercial
Vegetable Recommendations Guide Available at Local Extension Offices
You may obtain copies of the Commercial Vegetable
Recommendation Guide from
your local
Field Crop Insects - Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
New Field Corn
Registrations for Soil Insect Management 2002:
As you make plans to plant field corn, understanding the factors that favor soil insect pests can be used when making a treatment decision and selecting the best treatment option :
Seed Corn Maggot (SCM).
Since winter temperatures have been warmer than normal, we
are starting to find seed corn maggot flies laying eggs in recently plowed
and/or manured fields. Cool wet conditions at
planting, the use of manure and/or plowing under of green cover crops close to
planting all favor maggot problems. Depending on spring weather conditions,
most early planted conventional corn and all no-till plantings will be
susceptible to seed corn maggot attack. In addition to soil insecticides, seed
treatments have provided effective control. Hopper-box treatments containing diazinon or permethrin as well as
seed commercially treated with imidacloprid (Gaucho
or Prescribe) will
provide effective seed corn maggot control. A new 2(ee)
registration was issued on
Wireworms.
High soil organic matter, sod covers, and heavy grass weed pressure the previous season all favor wireworm populations. Fields having a combination of high organic matter and heavy grass weed pressure are the most susceptible to damage. Wireworm larvae spend multiple years in the larval stage and the larvae move up and down in the soil profile following moisture gradients. Therefore, good control is often difficult to achieve. Seed treatments containing lindane or permethrin will only control larvae feeding on the seed when population levels are low to moderate. They will not control larvae that have moved to the growing point of a plant and started to feed. However, Gaucho and Prescribe seed treatments have provided excellent control of both seed and seedling damage from wireworms under high population pressure. Soil insecticides including Regent, Force, Fortress, Furadan, Lorsban and Counter have provided control. All materials must be placed in-furrow to get effective control and applied at the higher end of the labeled rate. If Regent is used, fields can not be planted to leafy vegetables for one month, root crops for five months, or small grains and other rotational crops for 12 months following an application. The new 2(ee) registration for Warrior also applies to wireworm control and should be used at a rate of 1.92 oz/acre.
White Grubs.
In general, grubs are favored by a number of factors
including planting into double crop soybean stubble, old sod, hay, pasture or set-aside acreage. Overwintering
populations were higher this season and warmer soil conditions may have favored
survivorship. However, spring conditions as well as the recent cooler weather
may help to reduce populations. The most accurate way to measure the potential
for a grub problem is to sample fields for grubs before planting, but it should
be done before a field is tilled. The most accurate results will be obtained
when the soil temperatures at 6-inches deep are at least 45 degrees F. At each
site, sample one square foot of soil dug six inches deep. One to two samples
should be taken for every 10 acres with no less than 10 samples per field. A
treatment is recommended if you find 1-2 grubs per foot in heavy soils or 0.5 –
1 grubs per foot in sandy soils. Soil insecticides need to be placed in-furrow
to get effective grub control. Counter, Force, Fortress, Regent and Prescribe
will provide effective control. Remember, at planting insecticides are only
designed to provide control of grubs present at planting time. You should not
expect control of larvae present in August and September that resulted from
eggs laid in early July.
Black
Cutworm.
This insect is favored by late planting, broadleaf weed growth (especially chickweed) present before planting, poorly drained field conditions and reduced tillage. Rescue treatments can be applied for this soil insect if you are able to scout fields twice a week once leaf feeding is detected. If you are unable to scout and you have conditions favoring cutworms, a pyrethroid (Ambush, Asana, Pounce, Mustang or Warrior) tank mixed with a herbicide and applied close to planting has provided effective control. Pounce, Mustang and Warrior can also be applied as a liquid t-band application at planting for cutworm control. The granular insecticides Force, Lorsban and Fortress are labeled for cutworm control, but must be applied as a T-band to be effective. Pheromone traps placed in the field by mid-March can be used to determine when to look for cut plants as well as areas of the state most likely to experience economic levels. Look for pheromone trap counts in future reports.
Wheat.
Although we still find
spotty distribution of Barley Yellow Dwarf Virus (BYDV) in the state, aphid
management can play an important role in reducing losses from BYDV. It still
appears that the most important time to control aphids and help reduce problems
from BYDV is the first 30 to 60 days after plant emergence. Information from
The aphid causing the greatest amount of damage last fall
was the Greenbug. This aphid can be easily identified
by the green stripe down the center of the body. The most significant losses
occurred on the eastern shore of
|
#/Foot of Row |
Plant Height |
Time of Year |
|
20-50 |
4-6 " |
Fall - late Winter |
|
200 |
7 - 10 " |
mid-March |
|
300 |
18-20 " |
mid-April |
|
800 |
30 + " |
mid-May |
|
|
||
|
Greenbug Aphid with green stripe down the back |
||
Alfalfa.
During the last two growing seasons, alfalfa weevil populations have been higher than normal. A combination of warm winter weather and dry conditions could result in early feeding damage this season. Therefore, you should begin sampling fields for early feeding signs by the last week in March. Look for small larvae feeding in the tips of plants producing a round, pinhole type of feeding. Once you detect tip feeding, a full field sample should be taken. You will want to avoid treating fields too early since it may result in multiple applications. In general, no treatment should be needed before you observe 50% of the tips with feeding damage.
Precautions for Herbicide Use with Nitrogen
Applications to Small Grains - Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
It is common to add herbicides when nitrogen is applied to small grains and small grain-legume mixtures. These precautions are from manufacturer’s label:<
