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Extension Entomology

Month: March 2016

Wheat Aphids

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

We checked several wheat fields in north central Kansas this past week.  Once again, very few pests of any kind were detected.  As last week, there are a few aphids present, but not in any significant numbers.  With continued strong south winds, aphids will continue to migrate into the state.

greenbug

BCOA small

Alfalfa Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Once again we are in the midst of a typical Kansas spring with warm, bordering on hot, windy conditions interspersed with cold, windy conditions.  However, rainfall (or moisture in any form) has been pretty much lacking throughout south central and north central KS.  Again, as in most KS springs, the weather has variable effects on alfalfa and therefore, the alfalfa weevil.  Some fields are still showing effects of recent freezing temperatures.  Most of the yellowing/silver coloring in these fields is due to the weather.

Alfalfa freeze close

alfalfa freeze field

Fields that were sprayed before last week’s freeze still have live larvae but they are yellowish and moribund compared to larvae from fields not yet treated.

moribund larva

healthy larvae

However, fields not yet treated should be closely monitored as weevil feeding has been significantly slowed by the cold weather and has just started to become noticeable.

silvering alfalfa

This feeding will only intensify for about the next 7-10 days at temperatures ranging between 45-75°F.

Alfalfa Weevil Update

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Alfalfa weevils continue to be very active throughout north central Kansas, and the Kansas spring weather continues its usual erratic conditions.  However, the alfalfa weevil larvae continue to feed voraciously.  They have been slowed a little by the cooler weather but, remember, they do continue to feed 24/7, any time the temperatures are at least 48°F.  Much like the last few years, 2016 seems to be a good year for alfalfa weevils with most fields having multiple larvae/stem, at various developmental stages.

AW larvae

AW feeding damage

Wheat Insects

— by Dr. Jeff Whitworth and Dr. Holly Schwarting

We checked several wheat fields without finding much insect activity. There are a few greenbugs and bird cherry-oat aphids but not really enough to worry about yet. There are also many green lacewings and lady beetles present and feeding on these aphids which will help reduce populations.

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

 

 

Sugarcane aphid

This year, the warm weather has led to an early development of SCA on volunteer sorghum stubble along the Gulf Coast, something noted in a blog on Feb. 26. Alates (winged aphids) produced by these populations may have arrived in Kansas over the past week, as evidenced by infestation of sorghum in the greenhouse at the experiment station in Hays. Winged aphids can travel hundreds of miles in a matter of days when conditions are right, even though it is basically a suicide mission at this time of year. Based on the infestation patterns we had over the past two years, I have been advising early planting as the cheapest insurance policy – now I am not so sure. I have also been saying how lucky we were that the aphid arrived in Kansas so late in the season in both 2014 and 2015.  I should clarify here that it is not unusual for aphids to colonize our greenhouse in cold winter months, even though there is clearly no chance of them colonizing anything in the field.  It has been commented that we rear aphids here and that we could have been careless and caused the infestation.  I agree this cannot be ruled out entirely, but we have have been rearing SCA continuously for the last 2.5 years without any such occurrence.  In late January, when weather was much colder, we had Rhopalosiphum padi begin infesting both sorghum and millet  – and this aphid was not being reared on the station.  In fact, there has probably not been a single year over the past ten when we have NOT had spontaneous infestations of some aphid in the dead of winter; these have included green bug, Russian wheat aphid and Sitobion avenue, although R. padi is by far the most common.

What does this mean for the Kansas sorghum crop this year? It is hard to say, but two very different scenarios are conceivable. In the best case, these early populations will be brought under control by natural enemies either before they can spread to this year’s sorghum crop in south Texas, or soon thereafter by judicial insecticide treatments. Most of the southern crop will probably be planted with a seed treatment, so this may serve as a critical barrier to further population expansion, for a few weeks anyway. But there is also the risk of more aphids coming from Mexico, which is not unlikely given that management of SCA has generally been very poor south of the border. However, if management of SCA is effective in south Texas and this early outbreak either crashes naturally or is well controlled, it could mean that the inevitable resurgence of aphids actually occurs later in the season than it otherwise would have without the early outbreak, resulting in a Kansas situation not unlike the past 2 years where infestations develop late enough to have a reduced impact. This is our best hope.

In the worst case scenario, in the absence of a population crash, these early aphids could spread into newly planted sorghum across the south, a lot of which is just emerging right now, and then northward, putting all sorghum in Oklahoma and Kansas at risk from the seedling stage onward. Fortunately, it tends to be difficult for aphids to establish on small plants under Kansas summer conditions – excessive heat or a single punishing rainfall event can physically kill most of the aphids on a seedling. However, all aphid movement is highly weather-dependent, and the weather is looking more and more unpredictable with el nino conditions in effect, etc. We will continue to monitor the situation – if the worst case scenario seems to be unfolding as we approach planting dates in Kansas, it may be advisable to plant with an insecticide seed treatment, something I would not normally recommend. So lets hope for the best, and prepare for the worst.

Winged and wingless SCA
Winged and wingless SCA

-J.P. Michaud

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