Volume 11, Issue 6
May 2, 2003
Volume 11, Issue 6
May 2, 2003
Vegetables
Vegetable Insects
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Springtails.
As the first sweet corn and potatoes emerge from the ground, we have heard comments regarding high numbers of "flea beetles" present on the soil surface. On closer inspection, what folks are finding are garden springtails. They are tiny wingless insects with distinctive heads and a hump-backed appearance. Their name comes from a forked structure attached to the underside of the abdomen that acts like a spring to flip them into the air. This behavior gives them the appearance of tiny flea beetles or fleas. In most cases, they rarely cause enough damage to warrant control measures. Most springtails live in rich soil or leaf litter, under bark or decaying wood, or associated with fungi. Many are scavengers, feeding on decaying plants, fungi, molds, or algae. Springtails become abundant in wet soil and plant material. Most springtails do not survive in dry conditions. As the soil dries out, populations should decline rapidly.
Asparagus.
We have started to see an increase in asparagus beetle egg laying activity on spears. 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. Sevin, Lannate, Ambush, or Pounce will provide control.
Potatoes.
If Admire, Platinum
or Tops MZ Gaucho were not used at planting, begin sampling for recently
emerged Colorado potato beetle adults. A treatment should not be needed for
adults until you find 25 beetles per 50 plants and defoliation has reached the
10% level. Actara, Spintor
or Provado will provide good control of adults and
larvae. Although corn borer moth catches are light at this time, they are
experiencing extremely heavy flights on the Eastern Shore of Virginia.
Sweet Corn.
As soon as the first
plants emerge be sure to look for cutworm feeding damage. Variegated cutworm is often present in
early-planted fields. In general, this species is the first cutworm causing
damage to early-planted sweet corn. Regardless of the species, a cutworm
treatment should be applied if you find 10% leaf feeding or 3% cut plants in
one-two leaf stage corn. A pyrethroid or Lorsban will provide control. Fields should be treated
early in the morning or early evening when cutworms are close to the soil
surface to achieve the best control. In addition to cutworms, be sure to watch
for flea beetles on your earliest planted corn. In order to get an accurate
estimate of flea beetle populations; fields should be scouted mid-day when beetles
are active. A treatment will be needed if 5% of the plants are infested with
beetles. A pyrethroid or Sevin
will provide control.
Watermelons.
As soon as plants
are set in the field, you should begin scouting for cucumber beetles, aphids
and spider mites. The winter conditions should have helped to reduce cucumber
beetle populations; however, be sure to check for beetles on field edges near overwintering sites. Foliar products can provide good
cucumber beetle control; however, multiple applications of a pyrethroid or Sevin may lead to
spider mite outbreaks later in the season. So be sure to scout fields and only
treat if populations are causing damage. Admire and Platinum can also be
applied through the drip and should provide both beetle and aphid control.
There have been reports of low levels of aphids on plants in the greenhouse. If
plants are ready to set out, the best option is to check plants for aphids as
soon as they are set in the field. The treatment threshold for aphids is 20%
infested plants with at least 5 aphids per leaf. Fulfill, Lannate
and Thiodan are labeled on melons and will provide
melon aphid control. These materials should be applied before aphids explode.
We also have had a report from a consultant of very low levels of spider mites
in the earliest planted watermelons. Therefore, it will also be important to
sample for spider mites within a week of transplanting. If populations increase
gradually and you find a high percentage of immature mites, Agri-mek
has provided good control.
However, if
populations explode quickly and you are finding mostly adult mites, Capture, Danitol or Kelthane should be
used. No controls should be needed until 20- 30% of the crowns are infested
with 1-2 mites per leaf.
Tomato spotted wilt virus and Thrips Management (information from Tom Kuhar,
VPI,
“
Last year commercial
tomato producers were plagued by tomato spotted wilt virus (TSWV), particularly
in the warmer regions of
We know of one
commercially available tomato variety that is resistant to TSWV:Amelia VR, formerly HMX 0800, by Harris Moran Seeds http://www.harrismoran.com/products/tomato.htm. According to the company description, Amelia
VR combines an armor-plate disease package along with high fruit quality and
high yields. Multiple disease resistance, including TSWV and fusarium F3.
Firm and aromatic fruit, ideal for green and vine ripe
harvest. Crack tolerant skin.
Vigorous determinate plant with an excellent leaf canopy, and well adapted to
stake culture. This new tomato produces
a vigorous plant that can yield extra large and large-sized fruit. Harris Moran
field testing shows it performs best under moderate to heavy pruning. Dr. Herman Hohlt
(ESAREC, emeritus) tested this variety on the
Regarding TSWV
management, here is some information based on scientific research studies:
Reflective (silver) mulch has been shown to reduce TSWV disease incidence by
confusing and repelling thrips before they can orient
to plants. Early-season control of thrips,
particularly with a systemic insecticide such as imidacloprid
(Admire 2F) applied as a transplant drench can substantially reduce disease
incidence in tomato, pepper, and tobacco based on studies conducted in the
southeastern
Sandea
in Snap and Lima Beans -
Gowan has received a registration for Sandea in snap beans and lima beans as a preemergence herbicide. We have tested this product for a couple of years and it has looked good. It provides good control of common ragweed, pigweed, velvetleaf, smartweed, cocklebur, jimsonweed, and lambsquarters. Nutsedges will be suppressed. It provides no grass control. I would not apply Sandea with Pursuit, since they are very similar chemistries and as a result there is a good chance of injury. What does Sandea offer compared to Pursuit? Pursuit is not labeled for snap beans (due to injury). Sandea is better on ragweed and lambsquarters than Pursuit. The down side is that there are a number of rotational restrictions with Sandea, so you need to check your label. Sandea will not control Pursuit-resistant pigweeds. In fact since Sandea and Pursuit have the same mode of action, selection pressure for ALS-resistant weeds is the same whether Sandea or Pursuit are used. Use rate is 0.5 to 1.0 oz/A with the 0.5 oz/A rate recommended for sandy soils with low organic matter.
Diet Changes?
The USDA announced that for
the first time since the 1950s, the average American’s annual consumption of
flour has decreased to below 140 lbs, hitting 139 for the second year in a row. Trade association professionals from the
wheat industry attribute this to the Atkins diet phenomon,
which focuses on reducing carbohydrates and concentrating on protein. Americans consume 195 pounds of red meat,
poultry, and fish per year, 57 pounds higher than the 1950s. What are the long-term implications for wheat
produced at the farm level?
Field Crop Insects
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Alfalfa.
Alfalfa weevil populations are still below threshold levels
in most areas of the state, although development is ahead in
Field
Corn.
The first small-variegated cutworms were found feeding on spike stage corn this week. As you can see (table at end of newsletter), black cutworm moth catches have significantly increased. Looking at degree-day accumulations, we should not see significant cutting from black cutworm before May 15. Although variegated cutworms generally feed on leaves and can sometimes be found in the whorls of small corn, the same thresholds apply to both species. A treatment is recommended in 1-2 leaf stage corn when you find 3% cut plants or 10% leaf feeding. A pyrethroid or Lorsban will provide control.
Small Grains.
You should begin
sampling barley and early planted wheat for grass sawfly and true armyworm
larvae. Since sawflies can quickly clip heads in both crops, early detection is
critical. Be sure to shake plants to dislodge sawfly larvae feeding on the
plants during the day. In both crops, the treatment threshold for sawflies is 2
per 5 foot of row innerspace or 0.4 per foot of row.
The armyworm threshold is one per foot of row in barley and two per foot of row
in wheat. In barley, your control options include Lannate
or Parathion. In wheat, your options include Lannate,
Mustang, Parathion or Warrior. Remember, Parathion can only be applied by air
and has numerous set back restrictions.
2003 Black Cutworm Pheromone Trap Counts
Found on page 8.
Field Crop
Diseases -
Wheat.
Soil-borne wheat mosaic and wheat spindle streak mosaic
virus were detected in the
Barley.
Barley is heading all over the state and the spot blotch form of net blotch is evident on some varieties. The dark brown oval spots often have yellow halos and can be very numerous on susceptible cultivars. Usually we do not see enough damage to reduce yields.
Soybean
Cyst Nematodes.
It is still not too late to check for soybean cyst nematode. Soil test bags with the submission form can be purchased at the Extension offices. If you have a fax machine and need results quickly, test results can be sent via FAX if you provide the number on the Nematode Assay Information Sheet.
Sulfur Deficiencies and Sulfur-Magnesium Deficiences Show Up on Wheat and Barley - Richard W. Taylor, Extension Agronomist; rtaylor@udel.edu
Quite a few small grain fields located on sandy soils in
both
Photo 1. Field view of
barley showing sulfur (S) deficiency (tissue test indicated 0.11 percent S and
>5 percent nitrogen) on very sandy soil that had been fertilized with 20+
pounds per acre of S (Photo by R. Taylor).
Photo 2. Barley showing
sulfur (S) deficiency symptoms of stunted plants with general yellowing, but
beginning with newly emerged leaves (tissue test indicated 0.11 percent S and
>5 percent nitrogen) on very sandy soil that had been fertilized with 20+
pounds per acre of S (Photo by R. Taylor).
Photo 3. Barley showing
sulfur (S) deficiency symptom of severe stunting (tissue test indicated 0.11
percent S and >5 percent nitrogen) on very sandy soil that had been
fertilized with 20+ pounds per acre of S (Photo by R. Taylor).
Photo 4. Barley showing
sulfur (S) deficiency symptom of stunting and general chlorosis
or yellowing (tissue test indicated 0.11 percent S and >5 percent nitrogen)
on very sandy soil that had been fertilized with 20+ pounds per acre of S
(Photo by R. Taylor).
I think in some cases, the severity of the symptoms can be attributed to the very high N content of the tissue. With inadequate S uptake, the plants are unable to synthesize the S-containing amino acids and that limits the ability of the plant to make proteins and enzymes that do much of the work in the crop. In essence, the high N content worsens the S deficiency.
Why might we be seeing S deficiency? The severe winter weather and very cold spring limited root development while the excessive rainfall on the sandy soils that are usually involved leached S well below the crop rooting zone. Many of the fields are low in soil organic matter (SOM) that might supply S during mineralization. Also, cold spring conditions have inhibited mineralization of SOM. In the above case (Photo 1 to 4), S was applied along with N, but I speculate that rainfall quickly leached much of the S below the shallow rooting depth of the crop.
Other fields also with very sandy soil have been showing both S and Mg deficiency symptoms for both barley (Photo 5 and 6) and wheat (Photo 7 and 8). In some cases, the soil pH was about 6.0. A pH of 6.0 indicates that generally both calcium (Ca) and Mg soil test levels are adequate. So why is Mg deficiency showing up if soil test levels are adequate? Grasses, which both wheat and barley are, often are unable to absorb adequate Mg in cool, wet springs. In particular, this is seen in forage grasses. It leads to a condition in grazing cattle called “grass tetany” characterized by low blood serum Mg levels due to poor absorption of Mg by the grass under certain environmental conditions.
Photo 5. Barley showing sulfur (S) and magnesium (Mg) deficiency symptom of interveinal chlorosis or
yellowing (tissue test confirmed S and Mg deficiencies) on a loamy sand soil
near
Photo 6. Field view of
barley showing sulfur (S) and magnesium (Mg) deficiency (tissue test confirmed
S and Mg deficiencies) on a loamy sand soil near
Photo 7. Interveinal chlorosis of wheat
showing sulfur (S) and magnesium (Mg) deficiency (tissue test confirmed S and
Mg deficiencies) on a loamy sand soil near
Photo 8. Field view of
wheat showing sulfur (S) and magnesium (Mg) deficiency (tissue test confirmed S
and Mg deficiencies) on a loamy sand soil near
Can anything be done about the problem or should anything be done? A S, Mg, and potassium (K) containing fertilizer (KMag