Posts Tagged ‘18:27’

Agronomic Crop Insects – September 17, 2010

Friday, September 17th, 2010

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

Soybeans
We continue to get an occasional report and question regarding the need to treat fields for stinkbugs, soybean loopers and beet armyworms. Last week (Sept 9), Dr. Ames Herbert from Virginia Tech had a great article in their Ag Pest Advisory regarding the need to treat for soybean loopers: (http://www.sripmc.org/Virginia/)

“When helping growers make the decision on whether to treat a field for loopers we have to take the time to consider several components that influence the decision: the maturity of the crop, the health of the leaf canopy, and the number of loopers present. Let’s take them one at the time.

“In terms of crop susceptibility, after some long discussions with soybean agronomists (David Holshouser at VT and Jim Dumphy at NCSU), we came up with a rule-of-thumb as to when fields are safe, that is, worms can be left untreated with no fear of lost yields. We suggest that fields will need to be protected as long as the pods are still green and until the lower leaves are just beginning to yellow. This should correspond, more or less, with the R6.5 stage (10 days after R6.0 = full green seed). If leaves are beginning to yellow up the stem, not from drought but from the maturity process, and there are any pods on the plant that are beginning to yellow, the field is safe, no need to treat.

“Next we have to determine the health of the leaf canopy, robust, average, or thin. Each can tolerate different amounts of leaf loss before reducing yield potential. Robust fields (mid chest or higher) can tolerate a lot of feeding. Average fields (upper thigh to mid chest) can tolerate normal amounts of feeding. Thin canopy fields (mid thigh or below) cannot tolerate additional leaf loss. Also in this canopy assessment, we need to take a stab at estimating the current percent defoliation. This is not an exact measure, but your best estimate looking over the entire canopy top to bottom. The eyes tend to focus on those badly defoliated top leaves. Look beyond those and try to come up with an overall average. One thing we (and others) have noticed about soybean loopers is that their feeding is often in mid-canopy, not at the top like most other defoliators. All the more reason to inspect the entire canopy.

“Finally, how many loopers are present? There is not a single threshold because of all the factors we have just discussed, but a very general rule of thumb is that 15-20 or greater/15 sweeps constitutes a potential threat, depending on the maturity and canopy health. Thresholds vary quite a bit from state to state but this one falls pretty well in line with the other states. In considering these components, some fields will be no-brainers. Mature fields (late R6 or older) or fields with robust canopies and just a few loopers (10 or less/15 sweeps) can be left alone. On the other end of the spectrum, early R6 stage or younger fields with stressed, thin canopies and 15-20 or more loopers/15 sweeps need to be treated. This week in Virginia, there are a lot of fields in the grey zone (plants are in the mid to late R5 to early R6 stage, the canopy is average, the looper number is in the 12-18 range, and defoliation is less than 20%). I tell folks, if they can do this, to take a close look at these fields and make a mental image of the extent of defoliation. Revisit in 2-3 days (no longer) to see if it has greatly increased. If the percent defoliation has increased and loopers are still present at or near the threshold, treat it. If the level of defoliation has not increased much and/or the looper numbers have decreased, don’t treat. It all sounds pretty complicated and it is but taking the time to consider these components should help determine if a field needs to be treated some will and some won’t and allow growers to protect at risk fields but save money on safe fields.”

For those who are keeping track of the spread of brown marmorated stink bug, it has now been found in soybeans in all 3 counties in Delaware.

Small Grains
Be sure to sample fields at emergence for aphids, true armyworm and fall armyworm feeding. In past years, we have seen economic damage from all three insect pests.

With the heavy late summer worm pressure in soybeans and vegetable crops, it will be important to watch for “worm” damage to emerging plants. We have seen fields destroyed by armyworms in past years, especially in no-till situations. In many cases it has been true armyworm, although fall armyworm can also cause damage. Although there is no threshold available, you will need to watch for larvae feeding on small plants.

As you make plans for small grain planting, you should consider the following factors when making a treatment decision for aphids. In general, cooler summer temperatures with adequate rainfall followed by a warm, dry fall are conditions that favor aphid development in small grains, especially in early planted fields. Early fall infestations of the greenbug aphid (which cause direct damage to small grains as well as vector BYDV) are favored by cool, late summer conditions.

The main reason one would consider aphid control in the fall (except for greenbug aphid that causes direct damage) is the potential for Barley Yellow Dwarf Viral (BYDV) transmission. Plant pathologists in our area still do not feel that we are seeing a significant increase in the incidence of BYDV. However, in areas where you have seen BYDV in the past, where you are planting early, or you have seen direct damage by green bug aphids, a seed treatment that control aphids (i.e. Cruiser and Gaucho) would be a good control option. Information from Kentucky indicates that planting date is the most important factor determining the intensity of an aphid infestation. If you have a history of aphids transmitting viruses in the fall and you plan to scout for aphids, data from the south indicates that the most important time for controlling aphids to prevent BYDV is the first 30 days following emergence. The second most important time is the second 30 days following emergence. The following link to a fact sheet from Kentucky provides more information on aphids and BYDV in wheat (http://www.ca.uky.edu/entomology/entfacts/ef121.asp).

Orchard Grass
Although billbugs have been a significant problem in Virginia and West Virginia fields for the last few years, this is the first season that we have documented significant damage from this insect in the Delaware/Maryland Eastern Shore region. Dr. Rod Youngman from Virginia Tech has taken the lead in developing sampling and treatment timings for this insect. He has just posted a presentation on his website that gives good information on the biology of this pest, sampling methods, treatment timing and control options. (http://connect.ag.vt.edu/billbugipm2)

Various End-of-Year Items: Less Stress on Vegetables Now, Root Zone Temperature and Tomato Fruit Ripening Problems

Friday, September 17th, 2010

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

Figure 1 shows part of a tomato field that I wrote about a few weeks ago concerning how environmental stress (high temperatures and drought) on the plants greatly affected plant viability and fruit quality. Figure 2 is the same field today (Sept 22) with new green growth, lots of flowers and fruit, some of which will make it to harvest. This field has not been irrigated for the past 3 weeks and it is still growing well. It is amazing how vigorous the plants are without the stress of the environment and a heavy fruit load. Too often I think growers do not give environmental stress on their plants enough “credit” for some of the problems they see later in the season regarding fruit set and fruit quality.

One of the difficulties I have been having about some fruit ripening problems we see each year in tomatoes is why the problem seems to occur at about the same time of the season regardless of the maturity of the tomato plants (although plants with a heavy fruit load tended to have more problems than those with lighter fruit loads). One thing I was looking at was potassium (K) levels in plant tissue, which were greatly reduced in plants that were having the fruit problems. But why was the K and sometimes phosphorous (P) levels dropping in these plants at about the same time? One possibility I found was that when root zone temperatures (RZT) reached 82o F or greater the plants slowed their uptake of many nutrients including K, P and ,at times, calcium according to leaf tissue analysis. This phenomenon usually occurred earlier in the season and more severely in high tunnel tomato production systems. The problem is that sometimes as the levels of K decreased it was not always correlated with an increase in fruit problems. There appears to be additional factors involved besides lack of some plant nutrients. Would cooling roots somehow help off-set the heating of the root zone and could irrigation water from a well help this? From preliminary studies that I am still working on it appears the answer is no to both. Plots that were irrigated with well water vs. those irrigated from pond water seemed to have a slightly greater reduction in nutrient uptake, even though the RZT drop was greater temporarily.

One other study I worked on this year showed that I was able to reproduce “thrips” or “mite” feeding injury on tomato fruit with no (actually very low) thrips or mite populations being present (Fig 3). This was done by stressing plants that had a heavy fruit load. The more stressed the plants were (including RZT) the more the “thrips damage” showed up. Plants that were not stressed had little or no “thrips damage”; all plants had the same density of thrips and mites on them—very low. What then is causing this damage to tomato fruit? I still do not know. When I talk to hydroponic tomato growers they recognize this damage as nutrient imbalances and not as insect. This would make sense as the plants in the field become stressed the malady suddenly appears. I’ll talk more about this in winter meetings.

 

Figure 1. Stressed tomato plants, August 

 

Figure 2. Same plants recovered, September

Figure 3. Damage to tomato fruit usually attributed to thrips or mites, but with no thrips or mites present

Fall Plasticulture Strawberry Planting and Management

Friday, September 17th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Planting for plasticulture strawberries is progressing across Delmarva. Research has shown that planting should be completed by September 15 for the best chance at high yields. While this is certainly true where row covers are not placed until late fall, later plantings are still successful with the use of early placement of row covers. The goal is to have adequate development of branch crowns (4-5 for most varieties) by spring. For plantings that go in later in September, it will be necessary to place row covers much earlier in the fall to keep temperatures high enough to achieve adequate branch crown development; how early will largely depend on the weather. Certainly, if an extended cold period in October and November is expected, row covering is advised on late plantings. Be prepared however to remove covers during late “Indian Summer” hot periods. One advantage to these late plantings is reduced runner formation and corresponding reduced labor in removing runners.

Change in Pre-Harvest Interval for Dual Herbicide on Spinach, Reminder on Waiver

Friday, September 17th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

The pre-harvest interval for Dual Magnum on spinach has been changed from 40 to 50 days. Growers are reminded that a Special Local-Needs Label 24(c) has been approved for the use of Dual Magnum 7.62E to control weeds in spinach in Delaware, Maryland, New Jersey, Pennsylvania, and Virginia. The use of this product is legal ONLY if a waiver of liability provided by the local growers association has been signed by the grower, all fees have been paid, and a label has been provided by the association.

In Delaware, the Fruit and Vegetable Growers Association of Delaware is the entity that holds these labels and waiver forms. Contact Gordon Johnson, Extension Vegetable and Fruit Specialist, University of Delaware, for waiver forms and copies of the revised label:

Gordon Johnson
Carvel Research and Education Center
16483 County Seat Highway
Georgetown, DE 19947
General Phone: (302) 856-7303
Direct Phone: (302) 856-2585 ext. 590
Cell Phone: (302) 545-2397
Fax: (302) 856-1845
Email: gcjohn@udel.edu

Crop Rotation Planning and Revision

Friday, September 17th, 2010

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Fall is a good time for vegetable growers to plan or revise rotations. The following are some general thoughts on rotations.

Three years is the minimum rotation for crops in the same family or with similar disease profiles. Five or more years is recommended for vine crops. Field crops such as corn, small grains, and sorghum are good rotational crops. Soybeans may be a good rotation for some crops but not for legumes such as lima beans or snap beans.

Problems often arise where growers increase vegetable acreage without adequate ground for rotation. Base your acreage decisions on available fields that fit rotational schemes.

Where vegetables are the main income for a farm, consider using soil improving crops (green manures, biofumgant crops, soil improving cover crops) in lieu of standard field crop rotations. While some income will be lost on field crop revenues, there will be long term gains with improved vegetable yields.

Where rotations are tight, it is critical to consider some disease reducing crops in the rotation (mustard family and sorghums for example). Try to build up organic matter in these fields as this generally improves overall soil health.

Rotate vegetable families where possible. Do not rotate within a family (such as the bean family, vine crop family, or tomato family). Sweet corn is an example of a good vegetable rotational crop to break up disease cycles on many farms.

Vegetable Disease Updates – September 17, 2010

Friday, September 17th, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Nematodes in Veggies
Fall is the best time to soil sample for nematode pests such as root knot, lesion, and other plant parasitic nematodes. After fall harvest but before any fall tillage is done, take soil cores six inches deep between plants in the row. Samples should be taken in the root zone of the old crop. Twenty cores/ sample should be taken from random spots in the field and placed in a plastic bucket, gently mixed, and a pint of soil submitted for analysis. Large fields should be subdivided into blocks of 15- 20 acres each and sampled separately. Nematode test bags and instructions are available for purchase from the county Extension offices. Samples cost $10.00. Fall sampling for root knot nematodes is strongly recommended for fields that will be planted in cucumbers, watermelons, cantaloupes, lima beans or other high value vegetables where root knot could reduce production. Forms and instructions are also available on the web at http://ag.udel.edu/extension/pdc/index.htm. Just a reminder, as I mentioned last week, do not take nematode samples until we get some rainfall if the soil is very dry.

Fall sanitation
In vegetable production it is not a good idea to leave old crop residue in the field any longer than necessary. If the crop is allowed to survive after harvest, fungi that cause many diseases continue to increase on the surviving plants. This allows higher numbers of the fungi to potentially survive until next season. Sanitation (plowing or disking the old crop) will help prevent pathogen carry-over.

Lima Beans
To date, I have not heard about or seen any samples of downy mildew in lima beans. The weather has not been favorable for infection.

Vegetable Crop Insects – September 17, 2010

Friday, September 17th, 2010

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

Cabbage
Continue to scout all fields for harlequin bugs, beet armyworm, fall armyworm, diamondback and cabbage looper larvae.

Lima Beans
Continue to scout all fields for lygus bugs, stinkbugs, corn earworm, soybean loopers and beet armyworm. As a reminder, Coragen and Belt are now labeled on legume vegetables.
Belt label: http://www.cdms.net/LDat/ld8LJ005.pdf
Coragen label: http://www.cdms.net/LDat/ld8KF000.pdf

Peppers
Be sure to maintain a 5 to 7-day spray schedule for corn borer, corn earworm, beet armyworm and fall armyworm control.

Snap Beans
All fresh market and processing snap beans will need to be sprayed from the bud stage through harvest for corn borer and corn earworm control.

Spinach
Continue to sample for webworm and beet armyworm larvae. Both can be found in fields and controls should be applied when worms are small and before webbing occurs.

Sweet Corn
All fresh market silking sweet corn should be sprayed on a 2 to 3-day schedule for the remainder of the season.

Southeast Strawberry Expo

Friday, September 10th, 2010

November 8-10, 2010
Wyndham Virginia Beach Oceanfront
Virginia Beach, VA

For the first time ever, the Southeast Strawberry Expo leaves its home base of North Carolina, heading this year to Virginia Beach, Virginia. The Expo offers workshops, a farm tour, a trade show, and educational sessions. Current and prospective plasticulture strawberry producers from Maryland, Pennsylvania, and other states outside the Southeast will find a warm welcome, sessions oriented towards very much toward their conditions and needs, and many opportunities for interaction with other growers.

For more information about the hotel, travel to the Virginia Beach area, program updates, and registration, visit www.ncstrawberry.com. Email info@ncstrawberry.com or call 919-542-4037 for more information.

Regional Women in Ag Conference

Friday, August 20th, 2010

January 25-26, 2010
Dover Downs Hotel and Casino
Dover, DE

More information is available at: http://ag.udel.edu/extension/kent/womeninag.htm  
or contact Laurie Wolinski at (302) 831-2538