Posts Tagged ‘16:5’

Agronomic Crop Insects

Friday, April 18th, 2008

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

Alfalfa
Economic levels of alfalfa weevil larvae and pea aphids can both be found in alfalfa fields, especially in Kent and Sussex counties. When sampling for aphids and weevils, collect a minimum of 30 random stems throughout a field and place them top first in a white bucket. For aphids, you want to count the number present per plant as well as any that have dislodged from the stem into the bucket. In seedling stage alfalfa, a treatment should be considered if you find 5 aphids per stem. As a general guideline, you should consider a treatment in alfalfa less than 10 inches tall if you find 40-50 aphids per stem. The treatment threshold for alfalfa 10 inches or taller in height is 75-100 per stem. Although beneficial insects can help to crash aphid populations, the cooler temperatures have slowed their activity. As a general rule, you need one beneficial insect for every 50-100 aphids to help crash populations. For alfalfa weevil, you will also want to record the number of weevil larvae per stem. The following thresholds, based on the height of the alfalfa, should be used as a guideline when making a treatment decision: up to 11 inches tall – 0.7 per stem; 12 inches tall – 1.0 per stem; 13 – 15 inches tall – 1.5 per stem; 16 inches tall – 2.0 per stem and 17 – 18 inches tall – 2.5 per stem.

Field Corn
Black cutworm moth catches have significantly increased in a number of areas around the state, including Delmar, Leipsic and Selbyville (http://ag.udel.edu/extension/IPM/traps/currentbcwtraps.html). Moth catches of 9 to 15 moths per 7-day period have been associated with a moderate to high potential for cutworm outbreaks in field corn. Although pheromone trap catches can help determine when peak moth flight and egg laying occurs, they cannot predict the amount or magnitude of cutting that will occur. The presence of a major flight only means that the potential for an outbreak exists. Adverse weather, lack of adequate food for newly hatched larvae, predation, and disease can reduce larval populations. Scouting of seedling corn near the first cutting date is the best way to determine whether a problem exists. Even if a preventative treatment was used, all fields should be scouted at emergence for cutworm activity. As a general guideline, a treatment should considered in 1-2 leaf stage corn if you can find plants with 10% leaf feeding or 3% cut plants.

Small Grains
During the past week, we have received numerous calls regarding aphid management in barley and wheat. Based on research done in VA in past years, they found that small grains can tolerate a lot of feeding, especially lower in the canopy. As a general guideline, the treatment threshold for aphids in wheat and barley over a foot tall is 300 aphids per foot of row. Since we are past the time of barley yellow dwarf transmission (fall transmission is the most important), the next important time to consider aphid management in small grains is at grain head emergence. Since aphids feeding in the heads of small grains can result in a loss in test weight, it is important to look for aphids as soon as the grain heads emerge. As a general guideline, a treatment should be considered if you find 20 aphids per head and beneficial insect activity is low. Although beneficial insects can help to crash aphid populations, the cooler temperatures have slowed their activity. As a general rule, you need one beneficial insect for every 50-100 aphids to help crash populations.

We have also found low levels of cereal leaf beetle egg laying and the first small larvae in small grains in Sussex County. With the warm temperatures predicted for the end of this week, we could see an increase in larval activity by next week. The following information was taken from Dr. Ames Herbert’s fact sheet on cereal leaf beetle, which can be found at the following link: http://www.ext.vt.edu/pubs/entomology/444-350/444-350.html.

“Scout after peak egg laying and when up to 50% of eggs have hatched. If the population is mainly made up of eggs, then scouting should be at a later date when a minimum of 50% are small larvae. Samples should be taken at a minimum of 10 random sites in the interior of each field (avoid the edges). At each site, 10 tillers (stems) should be examined for eggs and larvae. This will result in 100 tillers (stems) per field being examined. Eggs may be on the leaves near the ground. Record the number of eggs and larvae counted at each sample site and calculate the total number of eggs + larvae found. Alternatively, stems can be examined at random while walking through the major portion of the field; again 100 stems per field should be examined. Scouting Frequency: Once egg laying has reached a peak, many fields will need only a single scouting for eggs and larvae. If the proportion of eggs in the sample is 50% or greater, then sample again in 5-7 days. Economic Threshold: 25 eggs and/or small larvae total per 100 tillers. This threshold is based on the number of eggs and small larvae present, rather than large larvae. Proper use allows fields at risk to be identified and treated in time to prevent significant yield loss.”

Very low levels of the first small grass sawfly and armyworm larvae have also been found in Sussex county. However, moth flights are behind compared to past years due to the cooler temperatures (especially night temperatures) over the past few weeks. If you treated a few weeks ago for aphids or winter grain mites, you will need to continue to scout for the “worm pests” since those sprays were applied too early to control armyworms and sawflies. In addition, if flag leaves have emerged already and you have typically applied a fungicide/insecticide application on wheat at flag leaf emergence, combination sprays applied this week and maybe even next week, may be too early to control armyworms and sawflies this year. In many years  one application of an insecticide, timed when fungicide applications were needed, has been enough to control the complex of insects present; however, delayed moth catches means that peak moth laying and egg hatch will not occur until later this year. As a reminder, this combination spray has generally not been done before the last week in April in past years. Therefore, it will be important to sample fields that were treated early to be sure you do not miss an infestation of these “worm pests”.

Grower’s Guide to Understanding DMI or SBI (sterol biosynthesis inhibitor Fungicides (FRAC Code 3)

Friday, April 18th, 2008

Andy Wyenandt, Assistant Extension Specialist in Vegetable Pathology, Rutgers University; wyenandt@aesop.rutgers.edu

The DMI (DeMethylation Inhibitors) or Sterol Biosynthesis Inhibiting (SBIs) fungicides belong to FRAC code 3 which include the triazoles and imidazoles. Some of these fungicides are commonly known as Tilt (propiconazole), Nova or Rally (myclobutanil) and Procure (triflumizole).

SBIs work by inhibiting the biosynthesis of ergosterol which is a major component of the plasma membrane of certain fungi and needed for fungal growth. Resistance by fungi to the SBI fungicides has been characterized and is generally known to be controlled by the accumulation of several independent mutations, or what is known as ‘continuous selection’ or ‘shifting’, in the fungus. In any given field population the sensitivity to the SBI fungicide by the fungus may range from extremely high (highly sensitive, i.e. will be controlled by fungicide) to moderate (partially sensitive) or low (mostly resistant to fungicide). This type of resistance is also known as quantitative resistance. With quantitative resistance there are different levels of resistance to the fungicide due to independent mutations, which is unlike the target mutations that occur in qualitative resistance associated with the QoI fungicides (FRAC code 11). Because different levels of resistance to the SBI fungicide may exist in the field, the fungal population may react differently to different application rates of the SBI fungicide. Hence, it is suggested that using a higher rate of a SBI fungicide, may improve control when lower rates have failed.

For example, let’s say that a powdery mildew population on pumpkin has 25% high, 50% moderate, and 25% low sensitivity to a SBI fungicide. If fungicide is applied at the low rate, only 25% of the population (highly sensitive) may be controlled, whereas if the high rate is used, 75% of population be been controlled. The main point here is that if low rates of SBI fungicides have been used and control seems to be weakening, bumping to a higher rate may improve control. Unfortunately, it is difficult to determine what proportion of the powdery mildew population is sensitive or not sensitive by looking at the field until you have begun spraying. The best advice, if you are using low rates and think those rates are not working like you feel they should, the rate should be bumped up to the high rate the next time the fungicide is sprayed, and if the high rate doesn’t work it may be safe to assume the fungal population has grown mostly resistant. Importantly, if the high rate fails, whether you bumped up to a high rate or started with one, and control does not seem adequate, do not continue to use the fungicide. Recognizing if and when fungicide chemistries are failing and when fungicide resistance is developing is critical to producing successful crops and why scouting on a regular basis, at least before and after each fungicide application, is important. Regular scouting can help reduce unwarranted and ineffective fungicide applications and help reduce wasted costs. Remember to always tank mix SBI fungicides with protectant (M) fungicides (i.e. chlorothalonil) to help reduce the chances for fungicide resistance developing. Always apply SBI fungicides according to label rates and resistance management recommendations and always be aware of the fungicide rates you are applying.

Vegetable Crop Insects

Friday, April 18th, 2008

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

Asparagus
The first asparagus beetles can be found actively laying eggs on asparagus spears. As a general guideline, a treatment is recommended if 2% of the spears are infested with eggs. Since adults will also feed on the spears, a treatment is recommended if 5% of the plants are infested with adults.

Cabbage
Begin scouting fields for imported cabbage worm and diamondback larvae. With the increase in temperature, we could see an increase in moth egg laying activity. As a general guideline, a treatment is recommended if you find 5% of the plants infested with larvae. If both insect species are present, Avaunt, the Bt insecticides, Proclaim, Rimon or Spintor have provided control. Radiant is now also labeled on cabbage for both insect species.

Peas
Be sure to sample peas for pea aphids as soon as small seedlings emerge. 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. Be sure to check labels for application restrictions during bloom.

Sweet Corn
As soon as plants emerge from the ground, be sure to sample fields for flea beetles and cutworms. 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.

Vegetable Diseases in the Greenhouse

Friday, April 18th, 2008

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Many vegetable transplants are being grown in greenhouses across Delmarva. Potential for disease can be minimized in many ways:

  • *use certified tested and treated seed (even organic vegetable growers can treat with hot water or bleach solutions)
  • *walls, benches, hand tools, pots and trays should be sanitized with 5% commercial bleach
  • *weeds should be eliminated
  • *new (or sterilized) potting mix should be used
  • *seedlings should be watered early in the day so that the foliage dries quickly and, if possible, watered at the seedling base to reduce moisture on leaves
  • *provide good air circulation and exchange in the greenhouse to minimize periods of high humidity

However, even after careful sanitation and good greenhouse management practices, disease may develop. Most fungicides are not labeled for greenhouse use.

The following table, which is modified from the Vegetable Management Guide 2008-2009 New England Region, is a good summary of available fungicide options and the diseases that they manage. Please note that Ridomil is not labeled for use in the greenhouse. Use only labeled fungicides or biofungicides. Read the label carefully because if a product is not applied properly, phytotoxicity may occur.

Follow this link for the table: \”Fungicides and Bactericides Labeled for Vegetable Bedding Plants (pdf)\”

Cold Effects on Early Transplanted Vegetables

Friday, April 18th, 2008

Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

The frost we had this week should remind growers that as you try to get a jump on the growing season, cold weather effects need to be considered. Over the years, many of our early plantings of summer vegetables have suffered because of early cold damage and inadequate provisions to protect plants.

There has been a tendency to risk earlier and earlier plantings as growers try to hit the early market.

Earliest plantings of watermelons, cantaloupes, summer squash, and tomatoes will begin in the next 10 days. First transplanting of crops such as peppers and eggplant will begin in early May. One of the characteristics that all of these crops have in common is that they are warm season vegetables that are sensitive to cold temperatures, both in the root zone and above ground.

Considerations for early transplanted warm season vegetables:

1. Choose the lightest ground that warms up quickly for early plantings. Plant higher sections in the field first. Avoid areas that receive any shade from woods or hedgerows. Early fields should be protected from extreme wind and should not have frost pockets.

2. Lay plastic mulch well ahead of time to warm soils. Black plastic mulch should have excellent soil contact. Loose mulch is much less effective in warming soils.

3. Consider using IR plastics that trap heat (green and brown plastics). Clear plastics can be used but weeds are an issue and a good herbicide program will be needed

4. Make sure that there is good soil moisture when forming beds and laying plastic because soil water will serve as the heat reservoir during cold nights.

5. Careful attention needs to be paid to hardening off warm season vegetable transplants that will be planted early. Gradual acclimation to colder temperatures will reduce transplant shock. Do not transplant tender, leggy plants or plants coming directly out of warm greenhouse conditions for these early plantings.

6. Use vegetative windbreaks such as rye. This will reduce heat transfer by wind. Consider using windbreaks between each plastic bed in early plantings.

7. Consider using covers to protect from cold and wind and to increase accumulated heat. This includes slitted and perforated row covers and floating row covers.

8. Watch extended weather forecasts and plant at the beginning of a predicted warming trend.

9. Monitor soil temperatures in plastic beds and do not plant if they are below 60°F. Soil temperature in beds should be measured at the beginning of the day when at the coolest. When soil temperature conditions are not favorable, wait to plant.

10. Avoid planting in extended cloudy periods, especially if plants have come out of the greenhouse after an overcast period. These plants will not perform well.

11. When transplanting, make sure that there is good root to soil contact and there are few air pockets around roots.

Transplanted warm season vegetables vary in their ability to tolerate adverse weather after being set out. Tomatoes will stop growth but will grow out without much damage once warm weather returns. Summer squash also handles adverse conditions fairly well. Watermelons will hold if they have been hardened off properly. Cantaloupes can be permanently stunted if exposed to excessively harsh early conditions. Peppers and eggplants will not put on any root growth until temperatures are warm enough. Remember that all of these vegetables are susceptible to frost damage and will be killed by a late freeze.

In years with cold, cloudy, windy weather after transplanting, we have had large losses of transplants in the field. In many fields considerable hand labor was used to replace dying plants and in some cases whole fields were replanted. It is critical to have warm soil conditions after transplanting to allow roots to grow out into the bed quickly. What happens in cold, cloudy conditions is that plants shut down physiologically. Little root growth occurs and the existing roots on the transplant do not function well. If there is any wind, plants lose more water than they can take up and they die due to desiccation. This is accelerated when the sun does come out – the first sunny day after an extended cold, cloudy period is when you will see the most wilting of weakened transplants.

Later on in the growth cycle, cold weather during flowering can lead to problems with pollination and fruit formation resulting in reduced fruit set and malformed fruits.