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Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevil feeding activity has slowed significantly in north central Kansas, at least south of I-70.  North of I-70, larvae are still developing and thus feeding, but even in the northern counties this feeding and resultant damage should be significantly reduced by the end of the next week.  There are still some small larvae but the majority of populations are pupating or have pupated.  Adult weevils are still hanging out in alfalfa fields and probably will until that 1st cutting, or temperatures get into the mid-80’s or warmer.

Ant and Termite Swarms

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

It is that time of year again when termites and ant colonies start producing ‘swarmer’s’.  Swarms of flying ants have already been noted in the last week.  After all of the moisture, and as the temperatures warm into the 70s°F and above, both ant and termite swarming will become more apparent.  Only the adult reproductives of both ants and termites have wings and can fly.  These flights, or more rightly probably called flutters, are of short duration and usually start mid-to-late morning as temperatures warm into the 70’s.  These swarms can contain up to thousands of winged individuals and often attract the attention of birds and other predators that take advantage of these poor flyers for an easy meal.  It is important to distinguish between ants and termites because termites can be very destructive of just about anything made out of wood while ants are more of just a nuisance.  The following can help distinguish between ants and termites.

 

For more information regarding ant and termite biology and control please see these publications:

ANTS – https://www.bookstore.ksre.ksu.edu/pubs/MF2887.pdf

TERMITES – http://www.bookstore.ksre.ksu.edu/pubs/mf722.pdf

 

Dormant Oils

–by Dr. Raymond Cloyd

Dormant oils are applied during winter in order to deal with insect and mite pests that survive the winter in overwintering life-stages, such as eggs or mature females. Instead of waiting until spring to initiate “control” measures, the application of dormant oils may be helpful in reducing costs associated with pesticide inputs (in this case, insecticides and miticides) later in the season (spring through fall). The advantages of applying dormant oils include: 1) a wide range of activity against most species of mites and scales—even the eggs; 2) minimal potential for resistance developing in insect and/or mite pest populations; 3) less direct and indirect harmful effects to beneficial insects and predatory mites compared to pesticides with long-residual activity; and 4) relatively low toxicity to humans and other mammals. The disadvantages of dormant oils include; potential phytotoxicity during the growing season and minimal residual activity or persistence.

Dormant oils are typically derived from paraffinic crude oil, and are the heaviest of the petroleum-based oil sprays with a low unsulfonated residue (Figure 1).

figure-1-dormant-oil-product

Figure 1: Dormant Oil Product

The unsulfonated residue is an assessment of the phytotoxic compounds remaining after distillation and refining. An unsulfonated residue >92% indicates a highly refined product with less potential for phytotoxicity. Dormant oils generally have a unsulfonated residue value <92%.

Dormant oil applications are primarily directed at killing overwintering pests including certain mites and scales (Figure 2),

figure-2-dormant-oil-product-label-information

Figure 2: Dormant Oil Product Label Information.

before they become active in the spring and are capable of causing plant injury. Applications are made during winter so as to minimize phytotoxicity to ornamental plants. A 2% to 4% application rate is generally recommended in late fall to early spring. Dormant oils have contact activity and either suffocate; by blocking the breathing pores (spiracles), or directly penetrate and disrupt cell membranes of exposed insect and mite pests. However, dormant oils have minimal residual activity once residues dissipate, so thorough coverage of all plant parts is essential.

Since dormant oils are applied to all plant parts, the overwintering stage of the insect or mite pest must be located on the plant. However, not all insect and mite pests overwinter on plants. For example, dormant oil applications are not effective against the twospotted spider mite (Tetranychus urticae) because the mite overwinters as a female in plant debris, mulch, or other non-plant protected places. In contrast, the spruce spider mite (Oligonychus ununguis) overwinters as an egg on plants, primarily evergreens such as arborvitae, hemlock, juniper, and pine; so the spruce spider mite is susceptible to dormant oil sprays.

Dormant oils are effective in killing the overwintering stages of scales, especially first and second instars or nymphs (=crawlers). For example, euonymus scale (Unaspis euonymi) overwinters as second instar nymphs or mature females; both life stages are susceptible to dormant oil applications. However, certain scales that overwinter as eggs such as oystershell scale (Lepidosaphes ulmi) and pine needle scale (Chionaspis pinifoliae) are more tolerant of dormant oil applications because the eggs are generally stacked or piled on top of each other. Subsequently, dormant oils may not penetrate and contact the bottom layer. As a result, additional insecticide applications are typically required after egg hatch.

An issue when using dormant oils is the potential for plant injury or phytotoxicity. Some plants, such as arborvitae, beech, redbud, and certain maples (Japanese, red, sugar, and amur), may be harmed by dormant oil sprays. Furthermore, the needles of Colorado blue spruce (Picea pungens) may be discolored or change from blue to green as a result of a dormant oil application. Phytotoxicity may be a problem when >4% application rates are used and/or when applications are performed in early fall before dormancy or in late spring at bud-break. Problems associated with phytotoxicity are less likely to occur when applications are made in early November through February, which is when most plants are completely dormant. In order to avoid phytotoxicity, always ensure the spray solution is continually agitated. Also, never apply dormant oils when temperatures are ≤32ºF. Dormant oils should be applied to deciduous plants when the ambient air temperature will stay above freezing for at least 24 hours. Evergreens, in general, are more susceptible to damage than deciduous plants, so it is best to apply dormant oils when temperatures remain above 40ºF over a 24-hour period although there is no quantitative evidence suggesting that applications made at <40°F will damage dormant fruit trees. In addition, general recommendations are that dormant oils should never be applied to plants that are stressed since stressed plants are more susceptible to phytotoxicity. For example, lack of moisture, extreme temperatures, and sudden drastic changes in the ambient air temperatures after spraying, prolonged windy conditions, and disease or insect infestations may predispose plants to phytotoxicity. However, there is no direct evidence indicating that dormant oils are harmful to stressed trees.

There is a general misconception that insect and mite pest populations are unable to develop resistance to dormant oils. However, this is not true. For instance, a Christmas tree plantation of Scots pine (Pinus sylvestris) trees was sprayed with dormant oils for more than 10 years in succession to “control” pine needle scale. Eventually, the scale population became more and more difficult to “control.” Why? Well, what was discovered was that the scale covers actually increased in thickness; making it difficult for the dormant oil to penetrate the outer covering and kill the eggs.

Preventative dormant oil applications may avoid dealing with abundant insect and/or mite pest populations during the season. Therefore, inputs from insecticide and/or miticide applications may be reduced, thus preserving the natural enemies of mites and scales, including; predators and parasitoids that may naturally regulate populations of these pests.

 

Alfalfa and Wheat “Worms”

–by Dr Jeff Whitworth and Dr Holly Schwarting

Wheat and alfalfa fields throughout south central and north central Kansas should be monitored for signs of defoliation.  Many pests can defoliate either crop this time of year, i.e. grasshoppers and flea beetles (usually around borders), and “worms”.  These larvae are most commonly armyworms, fall armyworms, and/or army cutworms.  Identification is important for these “worms” because armyworms and fall armyworms will feed until the temperatures cool into the mid-20’s or they pupate, whichever comes first.

armyworm

fall-armyworm

 

Army cutworms, however, are and have been hatching from eggs deposited by moths as they return from over-summering, probably in Colorado.

army-cutworm

These army cutworm larvae will feed a little this fall, overwinter, then start feeding again in early spring.  So, if the “worms” causing the defoliation now are relatively large, ½ inch or more, they are probably armyworms and/or fall armyworms.

 

We have been hearing about and seeing a mixture of both armyworms and fall armyworms (see pics below).  These small worms start by causing small “windowpanes” in wheat or alfalfa.  No army cutworm infestations have been verified yet.

small-worm-1

small-worm-2

windowpane-feeding_wheat

Flocks of birds in wheat or alfalfa fields in fall or early spring are often indicative of a “worm” infestation as the birds are feeding on the larvae.  Fields with 25-30% of the plants showing “windowpane” feeding need to be monitored frequently as these larvae consume more as they get larger.  Treatment should be applied before stands become threatened.  For more information on treatment thresholds and management options please see the Wheat Insect Management Guide: http://www.bookstore.ksre.ksu.edu/pubs/mf745.pdf

Sugarcane aphids still hanging on!

–The KSRE Field Crop Entomologists Team

Sugarcane aphid populations continue to persist in sorghum across much of Kansas, but cooler temperatures are slowing them down considerably. However, monitoring populations is still strongly encouraged as infestations can grow quickly if temperatures warm up. Winged aphids are moving from early planted sorghum fields to late planted fields, so pay close attention to whether infestations are winged or wingless. Wingless aphids have the potential to increase rapidly, but several factors, including presence of natural enemies, can help slow population growth. In all cases, be sure to monitor populations closely. Bottom line: scout often.

photo-sep-20-12-28-09-pm
Winged aphids (alates).

Yield loss due to aphid feeding can occur up through black layer. However, most losses caused by sugarcane aphid occur between boot stage and up through soft-dough (50% dry weight in the seed) stage; more data is needed to understand losses between hard dough and black layer, but seed weight (grain quality) and total yield may be reduced. Further details about sorghum growth and development can be found here (MF3234.pdf).

photo-aug-30-12-18-10-pm
Lady beetle eggs in a sorghum head.

Harvest of early-planted sorghum is underway, and late-planted fields are only a couple of more weeks from being ready (depending on weather conditions). Most decisions to spray for sugarcane aphid this time of year are aimed at avoiding mechanical issues associated with high aphid numbers and honeydew coating leaves and heads. Although buildup of honeydew can cause significant harvest problems, this is not an inevitable outcome. Weathering can reduce honeydew stickiness, so once grain is fully ripe, delaying harvest for a week or two may be an option, provided there is no indication of lodging. As lower leaves senesce or die off, aphids migrate to the upper leaves and eventually into the heads. We have observed this behavior in several fields this fall. However, colder overnight temperatures will significantly retard aphid growth and reproduction, and significant aphid mortality may occur before freezing.

Aside from honeydew and potential mechanical issues, lodging can also be associated with high aphid populations. It is important to understand that sugarcane aphid is not the only pest in sorghum this fall. We have observed high levels of 2nd generation chinch bugs feeding behind panicle leaf sheaths, which can also weaken stalks and cause lodging. In addition, from a plant physiology standpoint, during the last weeks of grain filling sorghum stems tend to shrink due to natural plant remobilization process, affecting final stalk strength.

When making a decision to treat so close to harvest, growers should consider four main factors: 1) overnight temperatures, 2) stage of crop maturity and potential yield, 3) aphid density, and 4) and the preharvest interval for registered insecticides. If the aphids have been heavy, but your grain has turned color, you may want to wait until the honeydew weathers to become less sticky before trying to harvest it. Read and follow the insecticide labels. For Sivanto and Transform, the preharvest interval is 2 weeks. Follow forecasted temperatures for upcoming weeks. Cooler nights will slow populations. We’ve observed aphids killed by 10 hours at 46F in a small lab study, but more data are needed to understand what low temperatures, for what period, will kill them under field conditions.

photo-sep-28-4-36-32-pm
Sugarcane aphids after exposure to freezing temperatures.

Again, monitoring fields and relying on more than a single sampling event will provide additional information for making a treatment decision. The only reason to treat aphids past black layer is to avoid potential harvest issues. Killing aphids this fall will not impact aphid populations next year in Kansas. This is a migratory pest and will not overwinter in Kansas.

Termites vs. Ants

–Dr. Jeff Whitworth and Dr. Holly Schwarting

Termites and ants have both been swarming intermittently for the past couple of weeks.  Both species usually start swarming in April in Kansas, but the cooler April temperatures seemed to have delayed this behavior for about a month.

termite swarm

Please make positive identification of any insects you suspect may be a pest, but especially ants and termites because there is an enormous difference in the amount of damage potential of termites vs. ants.  Note that although carpenter ants may nest in wooden structures, they will not cause the same degree of damage as a termite infestation.  Because of this, the cost of management for a termite infestation is much greater than carpenter ants.  For more information on termites and ants, please visit:

Termites: https://www.bookstore.ksre.ksu.edu/pubs/MF2887.pdf

Ants: http://www.bookstore.ksre.ksu.edu/pubs/mf722.pdf

Alfalfa Weevil Update

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils are very active in south central and north central Kansas. We sampled many fields from 14 to 17 March and found small to medium sized (1st and 2nd instar) larvae in every field. Infestation levels ranged from 30% to 100+%.

AW early instar

Cooler weather over the next three days should slow down egg hatch and larval feeding activity. However, it does not look like the predicted low temperatures will be cold enough to harm either plants or weevils. Then, with the return of warmer than normal temperatures next week, the weevils will again become very active. Thus, if the winds are calm enough and fields are at or greater than 30% infested, next week seems like the ideal time to treat for alfalfa weevils. Only pinprick holes in leaves and a little feeding on terminals is evident so far. This, however, will quickly change if weevils are allowed to feed in 65+°F temperatures.

AW feeding

 

 

Alfalfa Weevils

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevil larvae were first detected in north central Kansas on 3 March. Mr. Chuck Otte, Ag and Natural Resources Agent, also reported finding small larvae on 5 March in Geary County and Mr. Tom Maxwell, Ag and Natural Resources Agent, also reported finding small larvae and pinprick-sized holes in new alfalfa leaves on 9 March in Saline County. So, ready or not, alfalfa weevil larvae are here and, I would bet, many more will be hatching in the next few days to weeks. Alfalfa weevils will continue to hatch and larvae continue to develop any time temperatures exceed 48°F – and those temperatures have been much more common over the last few weeks than usual. Forecasts for the next 7-10 days also look for warm conditions. Thus, it looks like larvae will be emerging, and damage progressing, relatively quickly. Whether this warm weather will compress the alfalfa weevil larval feeding so that the damage is not as stretched out as usual remains to be seen. There are also many lady beetles present in the alfalfa fields we have checked as well as a few pea aphids. Treatment thresholds we use for alfalfa weevil insecticide applications are 30-50% infestation, i.e. 1 larva/2-3 stems.

For more information on alfalfa weevils, please visit:

http://www.bookstore.ksre.ksu.edu/pubs/mf2999.pdf

eggs in stem

Overwintering alfalfa weevil eggs in stem

alfalfa weevil

Early instar alfalfa weevil larvae

pinprick feeding damage

Pinprick feeding damage

 

Armyworms and Army cutworms in Wheat

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Several planted fields have already been sprayed to control worms.  What we have been seeing in south central and north central Kansas are a combination of armyworms (see pic) and fall armyworms (see pic).  Both of these species will do a similar type of damage.  When they are small they will feed on one side of the wheat leaf causing what is commonly called ‘window paning’.  As the larvae grow they devour more and more tissue until it may become quite noticeable and, under unfavorable growing conditions, may even severely reduce the stand (see pic).  Armyworm larvae will feed, probably for a couple more weeks, depending upon temperatures, and then pupate. If we haven’t yet had a hard freeze, they may emerge as moths and lay eggs in other wheat fields.  The first hard freeze will terminate armyworms.  Army cutworms, on the other hand, will not be terminated by the first hard freeze but will continue to develop all winter, feeding anytime temperatures are over about 45°F and will complete their development in the spring (see pic).  So, it is important to make proper identification of armyworms feeding in wheat as armyworms and fall armyworms will not be feeding throughout the winter and early spring but army cutworms will.

armyworm

 

fall armyworm

 

armyworm damage wheat

 

 

army cutworm

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