Posts Tagged ‘18:7’

WCU Volume 18, Issue 7 – April 30, 2010

Thursday, April 29th, 2010

PDF Version of WCU 18:7 – April 30, 2010

In this issue:

Vegetable Crop Insects
On Farm Adoption of Soil Health Practices as a Part of Integrated Pest Management for Vegetables
Resistance Management Strategies for Strobilurin Fungicides (FRAC Code 11)
Presidio Label Now Allows Application Through Drip Irrigation
Seedcorn Maggot Damage in Early Planted Cucurbit Fields

Its All About Light

Agronomic Crops
Agronomic Crop Insects
Small Grain Disease Update



Small Grain Disease Update – April 30, 2010

Thursday, April 29th, 2010

Bob Mulrooney, Extension Plant Pathologist;

Keep scouting wheat for foliar diseases. Stripe rust is still a concern and is present in the South. Warmer weather will favor the Septoria, Stagnospora complex that causes speckled leafspot and glume blotch as well as common leaf rust and tan spot.

Last week I inadvertently did not include Twinline fungicide from BASF as another choice for powdery mildew control and other diseases on wheat and barley.

Agronomic Crop Insects – April 30, 2010

Thursday, April 29th, 2010

Joanne Whalen, Extension IPM Specialist;

If economic levels of alfalfa weevil were present before harvest and you decide to cut instead of spray, be sure to check fields within one week of cutting for damage to the regrowth. If temperatures remain cool after cutting, there is often not enough “stubble heat” to control populations with early cutting. In some cases, damage to re-growth can be significant. A stubble treatment will be needed if you find 2 or more weevils per stem and the population levels remain steady.

Small Grains
During the past week, there has been a significant increase in populations of cereal leaf beetle larvae, especially in areas where adult egg laying has been abundant over the last few weeks. In many cases, larvae were very small (about the size of a pin-head) early in the week; however, they will quickly increase in size with the predicted warm temperatures. In addition, they can be found throughout the plant canopy so you need to look at the entire plant when sampling. Damage can occur quickly under these conditions so be sure to scout carefully for cereal leaf beetle larvae. The treatment threshold is 25 eggs and/or small larvae total per 100 tillers.

With the predicted warmer temperatures, we will also see an increase in true armyworm catches. Although true armyworms overwinter in our area, we can also get migrant moths from the South. Therefore, be sure to scout all small grains for armyworms at this time. Remember, on barley, head clipping can occur in a relatively short time. As a general guideline, the threshold for armyworms in barley is one per foot of row and for wheat one-two per foot of row.

In addition to armyworms, do not forget to watch for sawflies since larvae can be found in fields throughout the state. As a review, adult sawflies generally emerge in early April and begin to lay eggs in the leaf margins of small grains. Most egg laying is complete by early May but can be delayed by cooler temperatures. The first small larvae generally feed on the lower leaf blades and larval development takes approximately 21-30 days. Barley and wheat are both damaged by sawflies; however, during years of high population pressure, barley may experience more damage. Sawfly larvae prefer to feed on the stems and can be more damaging than armyworms. Stem clipping often occurs before leaf feeding is complete and/or the grain reaches physiological maturity. Since sawflies can clip heads quickly, be sure to scout carefully for larvae and watch closely for clipped heads. As a guideline, a treatment should be applied for sawflies when you find 2 larvae per 5 foot of row innerspace or 0.4 larvae per foot of row. However, remember if the number of clipped heads is twice the worm count for sawflies then it may be too late to treat for them.

Since aphids feeding in the heads of small grains can result in a loss in test weight, be sure to watch for movement of aphids into the grain heads. As a general guideline, a treatment should be considered if you find 20 aphids per head and beneficial insect activity is low. You need at least one beneficial insect per every 50-100 aphids to help crash populations.

Lastly, before treating for any insect be sure to check the days between last application and harvest when selecting a spray material.

Its All About Light

Thursday, April 29th, 2010

Gordon Johnson, Extension Fruit & Vegetable Specialist;

Production of high yields of quality fruit requires adapted varieties, close attention to disease and insect management, balanced plant nutrients, and good weather conditions. One of the other key areas that growers need to consider is light. Leaves require adequate light levels to produce sugars by photosynthesis. These sugars are then translocated into developing fruit. Sugars also provide the building blocks of other flavor components. With this in mind, a very important aspect of fruit management is to insure even light distribution throughout the plant canopy. This applies equally to small fruits and tree fruits.

The following are some considerations to achieve this even light distribution and to manage for the best combination of yield and fruit quality.

1) Play close attention to plant densities and do not overcrowd plants. While more plants often means higher yields, excess shading at high populations can lead to reduced quality. Crops like matted row strawberries bear the most fruit and best quality fruit on the edges of the row. In most fruit crops, fruits on the interior of dense canopies often have poorer color, reduced sugars, and poorer flavor.

2) Choose pruning and training systems that allow for even light distribution. In fruits such as peaches, this is achieved by pruning so that scaffold branches are arranged in a open form V or vase shaped form. In crops that use a central leader system such as apples, it means pruning to appropriate spacings and orientations between scaffolds to allow for good light penetration. In summer bearing brambles, this means having trellis wires arranged so that fruiting canes are to the outside where they can receive the most light and training new canes to the in the middle. Pruning canes higher will also allow for more light along the length of the cane, however, they should not be so tall that they shade neighboring rows.

3) Thinning fruiting material and thinning foliage is often necessary for good fruit quality, color development, and uniform ripening. Leaf thinning is practiced in grapes for this reason. Thinning of blueberry canes to remove old and weak material is another example as is detail pruning of many tree fruits to remove excess fruiting wood and allow in more light.

Seedcorn Maggot Damage in Early Planted Cucurbit Fields

Thursday, April 29th, 2010

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

There have been several reports throughout Maryland of early planted watermelon and cantaloupe fields with seedcorn maggot (SCM) damage. The damage to transplants is often thought to be just damping-off or some other soil disease, but growers need to split the stems of the plants to see if they contain any seedcorn maggots. Stems can contain 12-45 maggots. The stem often looks whole above ground level, but below ground the stem and roots are often shredded (Fig. 1). The seedcorn maggot is an early season pest of many different crops. Most of these crops are direct seeded, but transplants are also attacked. It is more of a problem during damp, cool periods and in fields with manure or decaying residue. This year has been perfect for the fly to cause damage as we had a very early warm up followed by a cool down. This caused growers to start earlier and it also caused more of the pest population to become active early.

The seedcorn maggot is a pale, yellowish-white maggot found burrowing into seeds or transplants. Full grown maggots are legless, about 1/4 inch long, cylindrical, narrow and tapered. Maggots lack heads and legs, but have small black mouth hooks in front (Fig. 2).

The seedcorn maggot spends the winter as a larva inside a puparium in the soil. When mature, maggots pupate and emerge in April and May, mate, and lay eggs on moist soil high in organic matter, near decaying vegetation or at the base of transplants. The adult, which resembles a small house fly, is a gray to brown fly about 1/5 inch long that can be seen flying over freshly worked soil or where manure has been spread.

Seedcorn maggot eggs hatch a few days after being laid, and small, white, tapered maggots begin to feed on and burrow into plants or seeds. The maggots usually feed for 2 to 3 weeks before pupating in the soil. Adults emerge from the pupal case in about 7 to 14 days, mate, and begin a new cycle. The entire life cycle is as quick as 21 days, resulting in 3 or more generations each year.

There are no rescue treatments for infested plants. Fumigation and soil insecticides do not do a very good job of reducing SCM infestations since the maggots attack the seedling just below soil level. Even the use of systemic insecticides does not completely control maggot infestation s if the weather is cool and damp. The best control is a warmed soil. My research has shown that when temperatures reach 71oF at a 4 inch depth under BLACK PLASTIC, flies will stop laying eggs and larvae do not survive well. Row covers over the newly set transplants will also work to keep flies from laying eggs in the transplants.


Figure. 1 Transplant damaged by seedcorn maggot


Figure. 2 Maggots inside split stem of cantaloupe transplant

Presidio Label Now Allows Application Through Drip Irrigation

Thursday, April 29th, 2010

Bob Mulrooney, Extension Plant Pathologist;

Valent USA Corp. just announced that EPA has approved the drip irrigation label for Presidio on pepper and other fruiting vegetables, curcurbits, brassicas, and leafy vegetables. This will be significant for growers that have had problems with Phytophthora capsici crown rot on pepper and summer squash. This application method will not control downy mildew on cucurbits or other foliar diseases. The Presidio label is available here.

Resistance Management Strategies for Strobilurin Fungicides (FRAC Code 11)

Thursday, April 29th, 2010

Andy Wyenandt, Assistant Extension Specialist in Vegetable Pathology, Rutgers University;

The strobilurin, or QoI, fungicides (FRAC code 11) are extremely useful in controlling a broad spectrum of common vegetable pathogens. You may know some of strobilurins as azoxystrobin (Quadris), pyraclostrobin (Cabrio), or Pristine (pyraclostrobin + boscalid, 11 + 7). All strobilurin fungicides inhibit fungal respiration by binding to the cytochrome b complex III at the Q0 site in mitochondrial respiration. Simply said, the fungicide works by inhibiting the fungi’s ability to undergo normal respiration. The strobilurin chemistries have a very specific target site, or mode-of-action (MOA). Although highly effective, fungicide chemistries like those in FRAC code 11, with a very specific MOA, are susceptible to fungicide resistance development by some fungi. For us, knowing the specifics on the technical jargon isn’t so important, its understanding what is at stake. So, if you read or hear someone speak about G143A resistance development to the strobilurin fungicides (where resistance is known in cucurbit powdery mildew and downy mildew, for example), you know what they are talking about and how important it is. So much so, if cucurbit powdery mildew develops resistance to one strobilurin fungicide it may develop what is known as cross resistance and become resistant to all other chemistries in FRAC code 11 — even if only one chemistry has been used!

How do we avoid the chances for fungicide resistance like this to develop? It’s simple, don’t let the fungus ‘figure out’ what it is being sprayed with and do this by rotating different fungicide chemistries (i.e. FRAC codes). Proper fungicides rotations are necessary when fungicides with specific MOAs are used in fungicide programs for controlling important diseases. That’s why it is important to follow a fungicides label precisely and be certain that some fungicide chemistries aren’t overused. All strobilurin fungicides should be tank mixed with a protectant fungicide, when possible. Remember tankmixing high-risk fungicides (i.e. FRAC code 11) with low-risk, protectant fungicides (FRAC codes M1-M9) helps reduce (and/or delay) the chances for fungicide resistance development. Never tank mix strobilurins together and never apply any strobilurin fungicide (either the same chemistry or different chemistry) in consecutive applications if stated by the label. Remember, azoxystrobin acts against the fungus the same way as pyraclostrobin does and so on. Even though you are spraying two different fungicides, each has the similar MOA and is acting against the fungus in the same exact way.

The publication”Fungicide Resistance Management Guidelines for Vegetable Crops in the Mid-Atlantic Region-2010” is available from the county extension offices or online at

On Farm Adoption of Soil Health Practices as a Part of Integrated Pest Management for Vegetables

Thursday, April 29th, 2010

Gordon Johnson, Extension Fruit & Vegetable Specialist;

Vegetable crops are susceptible to a number of soil borne pests. In particular, soil borne diseases such as Fusarium in vine crops and solanaceous crops, Rhizoctonia in bean crops, Sclerotinia in bean crops, Verticilium in solanaceous crops, Pythium in most vegetables, and Phytophthora in vine crops, solanaceous crops, and bean crops have major impacts on the productivity of important vegetable crops in Delaware . Nematodes are also an issue on many vegetable crops in the state (root knot on many vegetables, lesion on potatoes as examples). Current control practices include fumigation and the use of soil applied fungicides or nematicides. However, the most effective control is the use of long rotations with non-host crops. This has been the standard extension recommendation to reduce the economic impact of these diseases and reduce the need for chemical controls. Long rotations are difficult to achieve on many farms due to land limitations. This problem has been worsened by the pressure of development and the decrease in farmland for rotations.

Insects and slugs in soils are also issues in many vegetable crops that affect overall plant heath. Often, as with the case of seed corn maggots, cutworms, and slugs; practices that are recommended to improve soil health – such as use of cover crops and no-till planting in vegetable production – can increase problems with these pests. This limits the adoption of these practices.

A major limitation to overall plant health in Delaware vegetables is soil compaction. Not only does compaction directly affect root growth, it also leads to increased problems with soil borne diseases as compacted soils often stay wetter for longer periods. In processing vegetables, harvest schedules often necessitate the use of heavy equipment and trucks when soils are wet, leading to extensive, deep, and long term compaction problems. Soil health is compromised and performance of future crops is affected.

Weed competition is another important issue in vegetable production. Management of the weed seed bank in soils can be a challenge and should be considered in an overall soil health program. Many vegetable crops have limited herbicides available to manage weeds and there has been an increase in the number of herbicide resistant weeds. Notably, herbicide resistant pigweed is a major problem in Delaware vegetable production. Adoption of soil health building practices such as the combination of cover crops with no-till and strip-till vegetable production is often limited by these weed control challenges. Weed control in organic vegetable production has also been a major problem limiting organic acreage.

Overall vegetable plant health is greatly affected by plant nutrition and soil fertility. Delaware requires nutrient management plans on all farms. Part of this planning process is how to incorporate best management practices to reduce nitrogen (N) and phosphorus (P) losses. Manure and compost use needs to be balanced against vegetable crop requirements and existing soil levels (for P) often limiting applications. On the other hand, practices benefiting soil such as the use of winter cover crops are encouraged as they can recycle nutrients (N primarily) that would be otherwise lost. While not directly related to management of a specific pest, decisions related to soil fertility and nutrient management will have implications for soil health in general, and therefore needs to be included in soil health and IPM program for vegetables.

Water management is directly tied to practices that influence soil health and vegetable crop performance. This includes ways to increase water holding capacities of soils; and at the same time, how to maintain good drainage and aeration. Improving soil water holding capacities will reduce vegetable plant stress and improve overall plant health. In addition, water management is linked closely with many soil borne pests, particularly in relation to drainage, with disease organisms such as Phytophthora being a major problem with vegetables in poorly drained soils in Delaware.

There has been a renewal of interest in soil health in relation to vegetable production in Delaware especially where tight rotations are an issue. Fortunately, there has been considerable research related to cover crops, green manures, compost, organic matter, and rotations in the past 10 years and there is ongoing research in the region on the effect of different rotations and species to improve soil health and reduce soil borne pests. Vegetable cropping systems that incorporate cover crops with no-till production or that have limited tillage have also been studied in the region. Other research in the region on cover crops that can reduce soil compaction is of great interest. There has been research on soil nutrient and water management for vegetable crops but limited work on how these areas intersect with soil health. Delaware vegetable growers, large and small, can benefit by adopting specific practices that improve soil health and by incorporating these practices into an integrated pest management programs for their farms.

Starting in 2009 and continuing into 2010, there has been a coordinated educational effort in Delaware on soil health as a part of integrated pest management for vegetables with field demonstrations, classroom sessions, publications, and on-farm training sessions. This initial effort emphasized how to evaluate overall soil health on a farm, the use of compost, general cover crop and green manure crop use, and biofumigant cover crops use.

We will be continuing these extension programs on soil health as a part of vegetable integrated pest management (IPM) programs over the next 3 years. In this effort we will expand educational areas to include soil disease management, soil insect and slug management, soil compaction management, weed management, soil fertility and nutrient management, and soil water management as part of an overall soil health and IPM program for vegetable crops. The emphasis will be on the on-farm adoption of soil health practices.

We are seeking 20 vegetable farmers as potential cooperators, targeting farms that are experiencing soil health problems and that have tight vegetable rotations. Plans to improve soil health in problem fields will be developed working with each farmer. This will include recommendations for rotations, cover crop use, green manure use, compost use, manure use, other organic matter additions, biofumigant crop use, and tillage practices. These prescriptive plans will be implemented by each farmer and the effectiveness of suggested actions will be evaluated at the end of 3 years by using soil health assessment tests (before the program starts and after 3 years). The economics of using these methods will also be assessed.

Delaware growers interested in participating in this program should contact Gordon Johnson, Extension Vegetable and Fruit Specialist, University of Delaware, (302) 856-7303 office or (302) 545-2397 cell.

Vegetable Crop Insects – April 10, 2010

Thursday, April 29th, 2010

Joanne Whalen, Extension IPM Specialist;

With the predicted warm temperatures, you can expect to see an increase in egg laying by asparagus beetles adults on spears. As a general guideline, a treatment is recommended if 2% of the spears are infested with eggs. Since adults also feed on the spears, a treatment is recommended if 5% of the plants are infested with adults. For a picture of asparagus beetle eggs, adults and larvae please refer to the following link:

Continue to scout fields for imported cabbage worm and diamondback larvae. The first larvae can be found and sprays will be needed before they move deep into the heads. As a general guideline, a treatment is recommended if you find 5% of the plants infested with larvae. There are a number of effective materials available for worm control. Please refer to the following link for a list of materials

As soon as plants are set in the field, begin scouting for aphids, cucumber beetles and spider mites. When sampling for aphids, be sure to watch for beneficial insects as well, since they can help to crash aphid populations. As a general guideline, a treatment should be applied for aphids when 20% of the plants are infested, with at least 5 aphids per leaf, but before populations explode.

We are starting to see an increase in aphid populations. On small plants, you should sample for aphids by counting the number of aphids on 10 plants in 10 locations throughout a field. On larger plants, take 10 sweeps in 10 locations. As a general guideline, a treatment is recommended if you find 5-10 aphids per plant or 50 or more aphids per sweep. When sampling dry land peas, you may want to reduce the threshold, especially if they are drought stressed. Be sure to check labels for application restrictions during bloom.

Sweet Corn
Be sure to scout the first emerged fields for cutworms and flea beetles. As a general guideline, treatments should be applied for cutworms if you find 3% cut plants or 10% leaf feeding. In order to get an accurate estimate of flea beetle populations, fields should be scouted midday when beetles are active. A treatment will be needed if 5% of the plants are infested with beetles.