Critical Time for Black Cutworm Scouting – (John Obermeyer)
• Temperatures now favor corn and cutworm development.
• Corn cutting is likely as larvae get over ½” in length.
• Higher-risk fields for damage are those where weeds existed in March.
Warmer temperatures, accompanied with rainfall, has recently planted corn “jumping” out of the ground and emerged corn turning green. This acceleration in warmth will also speed the development of black cutworm larvae. Amazingly, moths continue to be captured in large doses, see the “Black Cutworm Adult Pheromone Trap Report,” to further pile on the record catches received since March 23.
If your field looked like this weeks ago, you should be scouting it for cutworm today
Accumulated heat units
Scout by inspecting 20 consecutive plants in each of 5 areas of a field (100 plants) for cutworms and feeding activity. Be sure to check areas that had an accumulation of weedy growth before or at the time of planting. Count and record the number of plants cut or damaged and determine the percentage of plants affected. Also collect black cutworm larvae (usually found near the damage, just beneath the surface during the day) and determine the average instar stage. A foliar, rescue insecticide may be necessary if 3% or more of the plants are damaged and black cutworm’s average larval instar is from 4 to 6. An instar guide is available inside the front cover of the Corn and Soybean Field Guide (a.k.a., pocket guide). Happy Scouting!
Asiatic Garden Beetle Grub Is Back – (John Obermeyer)
A call from Brian Warren, Frick Services of Whitley County, this past week alerted us to the fact that Asiatic garden beetle grubs are making their presence felt in sandy areas of fields in north central and northeastern counties. Notably, he was only finding damage in corn following soybean. Seed applied insecticides weren’t preventing the grubs from feeding on corn roots, more importantly the mesocotyl. Unfortunately there is no rescue treatment available. Damaged plants, if growing points aren’t compromised, may recover somewhat if grubs soon pupate (i.e., stop feeding) and ample moisture is available. Don’t let the size of the small grubs fool you, as Brian indicated, “they are like grubs on steroids.”
Japanese beetle and Asiatic garden beetle grubs compared
This "pouch" near the Asiatic garden beetle's mandibles are very distinctive of this species
Last week the University of Kentucky released an article documenting the discovery of a new disease of wheat in the United States called wheat blast. The article can be accessed at this link: <http://news.ca.uky.edu/article/uk-researchers-find-important-new-disease>. Wheat blast is caused by the fungus Magnaporthe oryzae (Pyricularia grisea), and has caused moderate to severe yield loss in wheat in Brazil since its detection in the mid 1980s.
Wheat blast was confirmed in Kentucky in 2011, and was limited to a single occurrence of the disease in one research plot in Princeton. No disease was confirmed in any commercial field in Kentucky in 2011. We have not confirmed the disease in Indiana to date, but this is a key time to scout for wheat blast. Symptoms of wheat blast are very similar to those of Fusarium head blight (FHB), and farmers and consultants should look for bleached heads at head emergence and early flowering. Wheat blast symptoms typically appear BEFORE symptoms of FHB, and heads will not have the orange or pink spore masses of the fungus that causes FHB. If wheat blast symptoms are suspected, collect several heads from each field and send samples to the Purdue Plant and Pest Diagnostic Lab (PPDL) for confirmation: <http://www.ppdl.purdue.edu/PPDL/index.html>.
So why are we detecting wheat blast in the U.S. now? Researchers at the University of Kentucky suspect that fungal evolution may be the cause of the find. Variants of the fungus that causes wheat blast also cause a blast disease on rice, and gray leaf spot on annual and perennial ryegrass. Perennial ryegrass is a common turfgrass, and annual ryegrass is a popular cover crop species. Mark Farman at the University of Kentucky has studied the wheat blast fungus found in Kentucky and determined that it is more similar to the fungus that causes gray leaf spot on annual ryegrass than the fungus that causes wheat blast in South America. This suggests that the detection in Kentucky occurred as a result of the fungus evolving and expanding its host range from ryegrass to wheat, rather than an introduction of the fungus from South America.
Research is ongoing at several universities in the U.S. to understand the disease and determine how to best manage it should the need arise. We currently do not know the potential impact of this new disease in U.S. wheat, but early detection and documentation of the disease in Indiana will help us to prepare management strategies for the future.
Early-Planted Corn Developing Slowly - (Bob Nielsen)
Figure 1. Late V1 seedling on 27 April in a field planted 4 Apr 2012 in westcentral Indiana
Freeze damage was reported to have occurred again on some winter wheat fields in White and Carroll Counties. Questions about the value of winter wheat as a forage have been asked. Dry matter yield increases as winter wheat matures, but forage quality declines. Past research conducted in Indiana indicates that the crude protein content of winter wheat at the boot stage is 9.9 percent on a dry matter basis and declines to 4.6 percent when harvested at soft dough. Dry matter digestibility likewise declines as the crop matures, 68 percent at boot stage and 55 percent at soft dough. These values are similar to expectations of forage quality with commonly used perennial cool-season grasses. Dry matter yield of winter wheat forage is much less in 2012. Previous studies indicated three tons of dry matter per acre were possible at flower stage, but this will not be attained his year. Producers need to check with their crop insurance agent about options they have if contemplating using the wheat growth as a forage.
We, including myself, were optimistic for this year’s wheat crop – timely planting, good fall growth, and a jump on spring development with warmer temperatures in March. However, many fields of wheat have been hit with a sucker punch (or three) – freezing temperatures after greenup, limited water for growth and nitrogen uptake (especially with dry fertilizers like urea), and even some barley yellow dwarf.
Indiana has experienced several weeks of cooler weather and nights that were near freezing in mid-April. Fortunately, most of our wheat (even the advanced wheat) was jointing at this time and the damage was only leaf tip burn (P&C 2012 issue 4). I did hear of a couple fields that showed freeze damage into the growing point (Figure 1) and lower stem (Figure 2). We thought we were out of the woods then temperatures last Thursday night (April 26) dipped below freezing again. Hard freezes (28°F) were noted in many areas in the northern third of the Indiana and wheat fields should be scouted now. Wheat was in the boot to heading stages when last week’s freeze came. The most severe period of damage usually occurs from the boot through flowering (P&C 2012 issue 4). I scouted several fields over the past few days with moderate to severe freeze damage (Figure 3).
Figure 1. Growing point killed by freeze – blacken growing point, but green leaves.
Figure 2. Freeze injury to lower stem – bruised appearance with a bend in the stem due to the tissue collapsing.
Figure 3. Severe freeze damage to a field in the boot stage. The sub-freezing temperatures settled into the field with the worst damage along the field edge. The temperatures were cold enough to freeze the flag leaves and the majority of the heads that were in the boot.
“Windshield” scouting is not suggested as many of the flag leaves were not burned with the recent freeze, so a drive-by will not always show the effects of the damage from the road (Figure 4). Younger wheat (prior to boot) will need to be split to determine if the growing point is dead (brown to blackish color). The leaves may still be green, but the growing point (the developing head) is dead (Figure 1). Emerged and emerging heads that are white have been frozen and the tissue is dead (Figures 4 and 5). Pale green portions of the head are questionable and further observation will be needed to determine the damage to the spiklets and anthers.
Figure 4. Flag leaf is green and undamaged, but the head that is in the boot was partially damaged from freezing temperatures. These symptoms are not visible from “windshield” scouting.
Figure 5. Emerging head that was in the boot when the freeze occurred 6 days prior to the picture. The awns and the head are whitish in color and the spikelets are dead. The spikelets on the lower, left side of the head were more protected and the damage is uncertain. Follow-up visits are required to determine the extent of damage to developing anthers.
The question is, “do I take it to yield or tear it up?” The decision needs to be weighed with the cascading effects on crop insurance, seed supply, crop rotation, manure application, calendar date, etc. I cannot address every scenario, but communication needs to be clear through all interested parties. Wheat is advanced for the time of the year, and assuming that harvest will be earlier, there will be greater opportunities for double-cropping soybeans further north than I typically recommend. A reduced wheat yield due to partial freeze damage may still work for those who could double crop soybeans.
Severely damaged fields from freeze or poor development have a few options for management: cut it for hay or wheatlage provided you have a market for it (see Keith Johnson’s article on forage quality), kill it with herbicide, mow it or till it. It is the first week of May, and we have plenty of time to establish a good crop of soybean or corn in these fields. The main point is to provide the best opportunity to establish a good stand and not to rush planting into wheat stubble or a matt of wheat residue without the proper planting equipment (i.e., planting “no-till” with equipment that isn’t set up for no-till).
Many options exist and should be explored for managing wheat that has been frozen or has low yield potential from other factors such as low water supply for nitrogen uptake, barley yellow dwarf, etc. Again, I highly suggest scouting wheat fields in the northern third of the state to assess any freeze damage and manage accordingly.
Pest&Crop Newsletter 2012, Issue 4. Freeze Injury in Wheat – S.N. Casteel. <http://extension.entm.purdue.edu/pestcrop/2012/issue4/index.html>.