Do Bugs Really Like it Hot? – (Christian Krupke and John Obermeyer)
An article being circulated in the popular news this week (originally appearing in USA Today) indicated that insects were flourishing throughout the country in this year’s record heat. We were contacted by CBS News and asked to comment, and may have disappointed the reporter by not fanning the flames on this particular story. The article featured quotes from several entomologists (mostly professionals in the pest control industry), that explained how insect development is temperature-dependent, so more heat = more bugs. Sounds simple and seems to make sense at first glance. But as many of you know, there is more to the story.
Caddisflies, an aquatic non-pest insect, have been abundant in our black light trap near the Wabash River in Knox County
If you’re an avid Pest&Crop reader, you’ve probably noticed the lack of insect pest related articles lately. Whereas, earlier in the year, we were sharing about the accelerated pace of insect development…most insects running 2-3 weeks earlier than historical calendar dates. Our colleagues in other systems, e.g., horticulture, fruits, vegetables, etc., were experiencing the same phenomenon. We know that if we were to just consider temperature, in general insects will develop more quickly and potentially have more generations in seasons that are warmer.
Of course, insects need more than heat. The lack of moisture that is causing so much concern in our cropping systems is also detrimental to insects – insects need free water to drink in many cases and they get that from standing water, dew and nectar. All are in short supply this year. The USA Today article is really just telling half the story to get the populace to envision massive hordes of mosquitoes, ants and spiders invading their homes. Although there are no hard data to back us up, we actually believe the record heat and drought has caused a dramatic decline in most insects this season, both pests and beneficials. It all starts with healthy, growing plants and those are in short supply in many areas. To put it simply, when crops are stressed, so are the pests that feed on them and their natural enemies.
Are you being driven buggy more in this heat?
Many of you are immediately thinking of one pest that is flourishing in this environment …spider mites. No doubt, in many soybean (and some cornfields), this 8-legged spider relative has shown its incredible reproductive potential in recent weeks. Two-spotted spider mite has been the fodder for our articles, and video, for the past several weeks and with good reason. Past droughts, most recently 1988, have taught us that hot and dry conditions will lead to population explosions of spider mites in field crops and this year is reinforcing that for us all.
All things are relative and experience counts for a lot when reacting to insect populations. When talking with a homeowner today about cicada killers flying around her frightened kids, facts are meaningless. Because she’s never experienced these intimidating (but non-aggressive) flying machines before, I’m certain she’d agree with the premise that insects are “worse” this year! We’re sure it had nothing to do with them recently moving to the country, being surrounded by trees (with cicadas), and recently constructing a soil berm in the backyard. Perfect for the cicada killer, not so for the homeowner.
Two-spotted spider mites have been well-covered by our publication and others in recent weeks. Most of those articles have dealt with soybeans, primarily because mites tend to be more problematic in beans than corn, and soybeans are still more “salvageable” in most areas. However, some irrigated corn fields in northern Indiana are infested with mites as well. One alternative to the organophosphorus insecticides (chlorpyrifos, dimethoate), is a miticide, trade named Comite (active ingredient propargite). Labeled for field and sweet corn, this product is best applied using ground sprayer if possible. Information from our colleagues in the Western Corn Belt certainly indicate that control of this species of mite is optimistic, but with good canopy penetration, should reduce the population enough to get the corn to the dent stage.
Dr. Bob Nielsen, Purdue Extension Corn Agronomist, visits a hot, dry corn field shortly after pollination to determine the success of kernel fill. This stressed corn field did get through pollination fairly well, but now many fertilized kernels are in a process of aborting or shriveling. The moisture level in these plants are so low, that the developing ears are flaccid and rubber-like. At this growth stage, and beyond, one can attempt to estimate grain yield by following procedures in this linked publication: <http://www.agry.purdue.edu/ext/corn/news/timeless/YldEstMethod.html>
Dr. Shaun Casteel, Purdue Extension Soybean Agronomist, shows symptoms of drought stress in a R3 growth stage soybean field. He goes through varying degrees of soybean stress, from yellowing of lower leaves to plant death. Most importantly, is how flowers and developing pods are lost, likely leading to yield losses.
Drs. Bob Nielsen and Shaun Casteel, Purdue Extension Agronomists, visit an irrigated corn field in the midst of a drought. While they transverse the interface from irrigated to moisture-starved corn they make several observations of plant response and the differences in air, leaf, and soil temperatures. This video certainly supports the old adage, "rain makes grain."
Irrigation Management In Time of Drought – (Lyndon Kelley, MSU Extension Irrigation Educator, Mike Staton, MSU Extension CURE Soybean Educator, and Steve Miller, visiting specialist Bio system and Agricultural Engineering)
Deck: Michigan and Indiana are in midst of the greatest agriculture water challenge seen for decades. Realizing the challenges and modifying Irrigation management allow producer to get the most from the resource available.
Several factors have led to lower summer water table and surface water levels:
Most irrigation systems in Michigan and Indiana were designed to supplement summer rainfall and do not have the long term capacity to keep up with drought condition crop water requirements. This can result in yield and quality reduction when water is restricted. The need for water is most critical now. Reducing irrigation to the level that is below basic crops water needs will jeopardize both the investment made on the applied water and purchased crop inputs. Corn exhibits the greatest yield reduction from drought conditions at pollination and the following two weeks.
Soybeans have little yield reduction in when drought conditions occur during the vegetative growth period as long as enough water is available for near normal plant growth. Adequate water is critical through blossom to prevent aborting of developing pods. Greatest yield advantage from irrigation is often achieved from R3 (beginning pod, one pod 3/16 inch long on one of the upper four nodes on the main stem having unrolled leaves) through R6 (full seed, one pod containing green seed that fills the pod cavity on one of the upper four nodes on the main stem having unrolled leaves. Water applied at R3 to R5 encourages flower and pod retention. This increases yield potential by increasing the number of seeds per acre. Irrigation water applied after R5 will primarily improve yields by increasing seed size.
So what can you do as irrigators?
For more information on irrigation scheduling see: <http://www.msue.msu.edu/objects/content_revision/download.cfm/revision_id.604557/
workspace_id.-30/#3Scheduling Tools.pdf/> or <http://www.extension.umn.edu/distribution/cropsystems/components/
This article will help soybean producers make profitable irrigation decisions.
I have not applied any irrigation water to my soybeans. Will I see an economic return by irrigating them at this point in the season?
Yes, especially if the plants are healthy and irrigation can begin at pod initiation. In general, the most important time to irrigate soybeans is from R3 (beginning pod, one pod 3/16 inch long on one of the upper four nodes on the main stem having unrolled leaves) through R6 (full seed, one pod containing green seed that fills the pod cavity on one of the upper four nodes on the main stem having unrolled leaves). Water applied at R3 to R5 encourages flower and pod retention. This increases yield potential by increasing the number of seeds per acre. Irrigation water applied after R5 (one pod with1/8 inch long seeds on one of the upper four nodes on the main stem with unrolled leaves) is also beneficial as it improves yields by increasing seed size. In fact, if soybeans can be watered only one time during the growing season, it should be at R5.
I began irrigating my soybeans in June to get them through the drought. Can I stop watering them now that we have received some rain?
You may be able to delay irrigation water applications due to recent rain but plan to apply irrigation water as necessary through seed fill (R6). Failure to continue irrigation may cause more stress on the crop than if no irrigation water had been applied. This is because soybean plants are able to adjust to soil moisture conditions by changing pod number and seed size. Plants may produce fewer and smaller seeds if irrigation is discontinued. The earlier irrigation applications may have also reduced rooting depth. Monitor moisture levels in the top two feet of soil closely and maintain the moisture level above 60% of the available water holding capacity throughout R6.
When can I stop irrigating soybeans without sacrificing yield?
Research from the University of Missouri showed that terminating irrigation too soon can cause yield losses of ¾ of a bushel per acre per day on a sandy soil. The Missouri researchers made the last application around September 20th which was well into the R7 growth stage. However, most universities recommend timing the final irrigation run so that the soil moisture level is near 60% of the available water holding capacity at the beginning of the R7 growth stage.
Precise timing of all irrigation runs, including the final run, requires a working knowledge of basic irrigation scheduling concepts such as the amount of water required for soybeans at various growth stages to reach maturity, available soil water capacity, allowable water depletions, soybean growth stages, effective rooting depth and estimating soil moisture status. Lyndon Kelley and Steve Miller have compiled a list of Irrigation Scheduling Tools <http://www.msue.msu.edu/objects/content_revision/download.cfm/revision_id.604557/
workspace_id.-30/%233%20Scheduling%20Tools.pdf/> that explain and utilize these concepts.
This article was produced by the SMaRT project (Soybean Management and Research Technology). The SMaRT project was developed to help Michigan producers increase soybean yields and farm profitability. SMaRT is a partnership between MSU Extension and the Michigan Soybean Checkoff program.