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Extension Entomology

Category: Field Crops

Field crop pest and beneficial organisms.

ALFALFA—Pea Aphids, Lady Beetles, Syrphid Fly

–by Dr. Jeff Whitworth

 

Pea aphids are still quite active throughout north central Kansas. However, most populations have been considerably diminished for several reasons, but now are mainly just a food source for various beneficial insects (fig, 1) as seen here, two species of lady beetles actively feeding on pea aphids, and (fig. 2) a syrphid fly larva that was also actively feeding on pea aphids.

 

Figure 1 Lady Beetle feeding on pea aphid  — (Cody Wyckoff)

Figure 2 Syrphid fly larva feeding on pea aphid (Cody Wyckoff)

Pea aphids are usually considered a pest when populations approach or exceed a treatment threshold, they can also be useful as a food source for beneficials until other aphid species increase, if they do, in other crops. Even though these aphids are still plentiful in most north central Kansas alfalfa fields, there was NONE that came anywhere close to a treatment threshold. Also, a very few alfalfa weevil larvae (fig. 3) can also be found, this is not unusual, or a cause for concern.

Figure 3 Alfalfa weevil larva (Cody Wyckoff)

 

Soybeans—Bean leaf beetles

–by Dr. Jeff Whitworth

Bean leaf beetles (fig. 6) overwinter in Kansas as adults. They are usually first found in late winter/early spring in alfalfa fields because as the temperatures start to warm these adults become more active and actually feed a little on alfalfa foliage. However, there are not enough to cause any problems in these alfalfa fields. However, every year they are impressive because of their super ability to detect the very first germinating soybean plants, whether volunteer or planted. They can apparently detect these early plants from many miles away. As these first germinating plants are found by these adult beetles from many different overwintering sites, they can do some quite noticeable leaf feeding damage (fig. 7). These plants are usually mainly on border rows as the adults fly to and start to feed on the first plants they find from distant overwintering sites. These oval/oblong holes can cause considerable concern, especially if only border rows are examined and growing conditions are stressful. Please remember these young soybean plants are very resilient at absorbing this early season defoliation without any subsequent impact on the plants or yield, as long as the defoliation is less than about 50% in the vegetative stages and good growing conditions return. These adult beetles then lay eggs in the soil and around the base of these plants where they hatch and the larvae feed on the roots/root hairs. These adults then emerge in mid-summer and start feeding on new leaves and/or, more problematic, sometimes on the pods.

Figure 6. Adult Bean Leaf Beetle (red color phase)

Figure 7. Damaged Soybean Seedlings (Cody Wyckoff

Alfalfa—-Alfalfa weevil, damage, aphids, lady beetle

–by Dr. Jeff Whitworth

Alfalfa weevil larval feeding damage seems to be almost finished (fig 1.) throughout north central Kansas, for one of the following reasons: some larvae were killed naturally a few weeks ago due to the freezing temperatures, some were killed by insecticide applications, and some have just developed  to the pupal stage and thus quit feeding. There are still a few active larvae (fig. 2) however, most remaining weevils are mature larvae, but there are also a very few younger ones (i.e. note the tiny larva that just hatched, at the tip of the pencil), plus a few pupae and adults.

Figure 1. AW feeding

 

Figure 2 Various stages AW larvae (Cayden Wyckoff)

Aphids are still present (fig. 3), but in tremendously reduced numbers, also probably for the same reasons as the factors that decimated the weevils, but plus–there are significant numbers of lady beetle pupae (fig. 4) and adults (fig. 5). This means there were significant numbers of lady beetle larvae previously feeding on those aphids. Hopefully, these ladybeetles will survive and move to any fields wherever they can find pests to feed on during the rest of the growing season.

Figure 3. Aphid (Cayden Wyckoff)

 

Figure 4. Lady Beetle pupae (Cayden Wyckoff)

Figure 5. Adult Lady Beetle (Cayden Wyckoff)

Many alfalfa fields have already just been/or are currently being, swathed throughout south central and north central Kansas. This should take care of any remaining alfalfa weevil larvae. However, it may allow some stem feeding, often called “barking”, by adults especially under the windrows and may continue until temperatures warm up into the 80’s.

Alfalfa

–by Dr. Jeff Whitworth

Much of the alfalfa throughout north central Kansas was significantly affected by last week’s freezing temperatures, as previously noted. This is especially true of older, less robust stands, as indicated by the plants in the lower left portion of fig.1. Sampling these freeze-affected

Figure 1 Alfalfa affected by the freeze (by Cayden Wyckoff)

areas with a sweep net revealed only very few live alfalfa weevil larvae, i.e. an average of 1 live larvae/10 sweeps. However, the less freeze-affected plants (upper right portion of fig. 1) had a much more significant infestation, i.e. these areas averaged 26 live larvae/10 sweeps. The vast majority of alfalfa weevil larvae detected this week were mature larvae, and many were actually on the ground, see Fig. 2. probably preparing to pupate, as a few new adults were also detected, again, see Fig 2.

Figure 2 Mature Alfalfa weevil larvae, new adult AW plus aphids and Lady beetle larva (by Cayden Wyckoff)

Figure 3 Aphids and lady beetle larvae (by Cayden Wyckoff)

 

Aphid populations, both pea, see Fig. 3, and cowpea, seemed to have dramatically declined also. This is probably a combination of the freezing temperatures coupled with a healthy population of lady beetle larvae, see Fig. 3, which have been voracious feeders on these aphids.

 

Challenges for Applicators concerning PPE

–by Frannie Miller

This growing season may be a challenge for producers/applicators in more ways than one. With the critical need for N95 respirators for health care workers, it is anticipated that applicators may experience a shortage of personal protective equipment (PPE) that will be available to use this growing season if not previously purchased. It is important to remember pesticides may not be applied without the label-required PPE. The Environmental Protection Agency has not issued any exemption or relaxation of the PPE label requirements, therefore some herbicides, fungicides, and insecticides you plan to use may require the use of N95 type respirators.

 

It is important to review the labels of products which are key to your operations and plan accordingly. If required PPE is unavailable for purchase, users may need to select alternative products or management methods. Research to see if there is a product available with the same active ingredient, whose formulation type reduces the need for respiratory protection. The other alternative is applicators are allowed to use more protective gear, so if you have a half or full-face respirator with a N95 filter that you have had fit-tested and received a medical evaluation to use this may be a good alternative.

 

Do not put yourself at risk by not following the label PPE requirements because you are having difficulty finding PPE. This could potentially add to the need for medical care and is in direct violation of the label, so please have a plan for how you will deal with this issue.

 

Pea Aphids/Cowpea Aphids

–by Dr. Jeff Whitworth

The recent cold weather also played havoc with these aphids (Fig. 3). However, many aphids, in untreated fields, were just “knocked off” or left the plants and are still alive, but in the leaf litter or residue under the foliage. There are also lady beetle larvae feeding on these aphids so, hopefully, these aphid populations won’t come back as dense as they were previous to the cold weather.

Figure 3. Pea and Cowpea aphids (picture by Cayden Wyckoff)

 

Alfalfa Weevil

–by Dr. Jeff Whitworth

Alfalfa weevils have been, and are still, very active throughout south central and north central Kansas during the last few days, even through the cold weather. However, just as the alfalfa plants have been variously affected by the recent cold weather, so have the alfalfa weevil larvae. The plants shown towards the middle of this picture (Fig. 1),

Figure 1Alfalfa freeze damage (picture by Cayden Wyckoff)

had the upper part of the foliage killed by the recent cold temperatures, as were the larvae in that foliage (Fig. 2).

Figure 2 Dead and live AW larvae (KSU Extension Entomology)

The adjacent plants were not as seriously affected and thus, neither were the larvae in those plants.

Thus, each field needs to be monitored at least weekly, even those fields already treated. Nevertheless, please — always remember, to follow all label directions for whatever product applied, especially as far as reentry, PHI, etc.

 

 

Aphids

–by Dr. Jeff Whitwoth

Every field sampled throughout North Central Kansas last week had pea aphids (fig. 3) and many had scattered infestations of cowpea aphids. Pea aphids are usually considered more of a cool weather insect while cowpea aphids more of a warmer (i.e. later in the season) insect, so that just illustrates the weather roller coaster we have been experiencing this spring. Treatment recommendations for pea aphids will probably work for cowpea aphids and/or mixed populations, which calls for 50+ aphids/stem, to justify an insecticide application.

Alfalfa Weevils

–by Dr. Jeff Whitworth

Alfalfa weevil activity has increased significantly in the last week throughout North Central Kansas. The recent warm weather has really stimulated egg hatch thus there are large numbers of very small 1st instar larvae just starting to feed, plus older, larger larvae (fig. 1) that have been feeding for a week or so. However, some fields have very low infestation levels, while others have already reached the 100% infested level. Recent freezing temperatures appeared to have killed some top growth in some fields, which can be mistaken for insect damage.

Thus, sampling each field is always prudent, but even more so this year. We have gotten many questions recently about the predicted cold weather and its effect on the weevils, but remember, alfalfa weevils are cool weather insects. Temperatures into the mid 20’s for a couple hours may kill small larvae, as we saw in 2018, but probably won’t affect the eggs or adults. Then, anytime the temperatures are over about 45°F, the larvae feed and do so 24/7 as long as temperatures are above 45°F. Many fields were treated this week and probably should be whenever the treatment threshold is reached as the predicted temperatures for the next 10 days looks like it will slow the feeding activity down but probably not be cold enough to kill very many larvae. Have also gotten the question about spraying for army cutworms and that effect on alfalfa weevils. If both occur at threshold or one or the other does and you make an application of an insecticide you should get pretty good control of both. However, remember, cooler weather will slow down the effect of the insecticide.

 

Also, check this super neat picture of biological control at work (fig. 2). A turkey harvested by a Kansas youth hunter on 6 April had a crop completely filled with large army cutworm larvae.

 

Wheat Update – armyworms, grasshoppers

–by Dr. Jeff Whitworth

Some fields have already established good stands of wheat this fall. However, there are also some pretty well established fields of volunteer wheat (see pic provided courtesy of Jay Wisby). There have been reports of armyworms and grasshoppers causing concern in some wheat fields that are struggling because of lack of moisture, but the recent cold weather should control both armyworm and grasshopper feeding.

 

 

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