INSECTS in FIREWOOD (Entfact 626) rarely cause any problems.
Recent reports of a handful of cases of aflatoxin contamination in stored corn in Kentucky and a neighboring state provide an opportunity to review some points about mycotoxins in corn. The drought conditions that occurred during much of the mid- and late summer last year could have set up conditions that resulted in mycotoxin contamination. Improper drying or cooling could have lead to the development of mycotoxins during storage. Two groups of mycotoxins are of greatest concern in stored corn: aflatoxins and fumonisins.
Aflatoxins
Produced by the fungus Aspergillus flavus, aflatoxins are potent liver toxins and carcinogens in
animals, and may also be human carcinogens. Because of its toxic potency, aflatoxin levels in food
and feed are highly regulated by the U.S. FDA, at the level of parts per billion. Aflatoxin
contamination in corn is uncommon in Kentucky, although occasional incidents do occur and can
create significant economic losses for individual producers. Severe drought and hot weather
during grain fill can favor contamination, resulting in infection of the grain by A. flavus and
the subsequent production of aflatoxin. Field damage to kernels from insects or birds can also
increase aflatoxin risk. If corn is not dried or cooled quickly enough to control grain moisture
and temperature and/or if it is stored in certain conditions, mold growth can flourish. More
information on a variety of aflatoxin-related topics (grain drying and storage tips, permissible
levels for livestock feeds and human foods, sampling for testing purposes, effects of aflatoxins
on livestock, and dealing with aflatoxin contamination of corn) are available in the Extension
publication, Aflatoxins in Corn, available online at:
http://www.ca.uky.edu/agc/pubs/id/id59/id59.pdf
Fumonisins
These mycotoxins occasionally can be found in Kentucky corn. These are toxins produced when certain
Fusarium fungi infect and colonize the grain. Horses, swine, rabbits and catfish are the most
sensitive species, though other livestock species can be affected at high enough levels. Drought
stress prior to or during silking is sometimes associated with Fusarium kernel rot fumonisin
contamination. Damage to kernels during maturation from birds or insects is also associated with
contamination. Damaged, Fusarium-rotted kernels typically contain higher fumonisin levels than
intact, healthy grain. This explains why corn screenings are often associated with animal
toxicoses attributed to fumonisins and underscores the importance of cleaning contaminated corn
prior to storage. More information on fumonisins can be found in the Extension publication,
Fumonisins, Vomitoxin, and Other Mycotoxins Produced in Corn by Fusarium Fungi,
http://www.ca.uky.edu/agc/pubs/id/id121/id121.pdf
Risks in 2005 Corn
Aflatoxins and fumonisins both are most likely to occur in corn during droughty growing seasons, which
was characteristic of many areas in Kentucky last year. Timely, hurricane-related rains and cool
nighttime temperatures in 2005 may have allowed fields to escape pre-harvest mycotoxin
contamination. However, storage conditions that allow molds to develop in the bin can allow low
levels of kernel infection by A. flavus and Fusarium fungi to develop into a contamination
problem.
The rule of thumb to avoid mold growth during storage is to dry corn to at least 16% moisture within 24 hours after harvest and cool to air temperature within 48 hours after drying. Corn in good condition must be further dried to 15, 14 or 13% moisture to be stored safely for 6, 9 or 12 months, respectively, and cooled to 60°F as soon as possible during the fall. These moisture limits are dictated by the way corn interacts with it's environment (see Figure 1). Corn in good condition will store safely at a relative humidity level of 65%, which is dry enough to retard the growth of storage fungi. Damaged corn and/or corn in poor condition should be dried an additional point or two (=60% humidity) and cleaned to protect grain quality.
Figure 1. Safe storage conditions for corn based on relative humidity levels at different moistures and temperatures.
Last fall's high energy prices and low grain prices coupled to set up some situations where corn was not dried thoroughly or to low enough levels that were safe for the corresponding storage period. Farmers were faced with a decision whether to let the crop dry in the field (and bear the cost of increased harvest losses) or harvest at 20 to 25 % moisture and pay 15 to 30 cents per bushel to dry it with LP gas at $1.50 per gallon. The additional energy cost required to dry corn to moisture levels below the standard market level of 15.0 or 15.5 % are best viewed as a storage/risk cost, which can normally recovered by wise marketing decisions.
Last fall's harvest situation also led many farmers to store corn above the top ring of their bins. Grain filled to the peak creates more resistance to airflow in the bin center and may not have been cooled thoroughly. It's always best to unload the top cone of grain in bins shortly after the rush of harvest to form a level (preferred) or v-shaped (second best) surface for improved airflow through the center of the bin and in the headspace. Coring bins removes the majority of fines and broken grain that tend to accumulate near the bin center and choke airflow, so this practice also helps aeration fans work more efficiently.
A few folks have speculated that some grain is out of condition because of the warmer-than-normal temperatures last fall, but a comparison with long term average weather data suggest otherwise (Table 2). From hourly data, opportunities that were available to cool grain below 10°F of the 50-year average were determined for Bowling Green, which is near the state-wide average. Each month last fall there were abundant opportunities to cool grain below the long-term average. The challenge for most producers was deciding when these opportunities were present! For this reason, producers are encouraged to consider installing automatic fan controllers on their storage bins and program them each month to select fan operation opportunities based on air temperature to help them protect grain quality.
Table 2. Comparison of average monthly temperatures in Bowling Green, Kentucky with those observed this year and opportunities to run the fan when temperatures were 10 degrees below the 50-year average. (From UK Agricultural Weather Center: http://wwwagwx.ca.uky.edu)
| Month | Temperature, °F | Hours of potential fan operation | |
|---|---|---|---|
| 50-year average | '05 average | ||
| Sept. | 68 | 72 | 193 |
| Oct. | 57 | 58 | 232 |
| Nov. | 46 | 48 | 178 |
| Dec. | 37 | 34 | 308 |
The bottom line on preventing mycotoxins in stored corn is to be knowledgeable of proven management practices. A summary list of storage tips is available at http://www.ca.uky.edu/agc/news/2001/Oct/storage.htm. More detailed information is provided in the chapter on Harvesting, Drying and Storing Corn In: A Comprehensive Guide to Corn Management in Kentucky (ID-139), which is available at http://www.ca.uky.edu/agc/pubs/id/id139/harvesting.pdf.
For information about corn pests, visit
"Insect Management Recommendations".
Potato leafhoppers can deliver a powerful punch to spring-seeded alfalfa. Fortunately, there are effective management tools but you have to swing before the leafhoppers land their punch. The swinging starts with the 15"-diameter sweep net that is needed to sample these little insects. Five sets of 20 sweeps from randomly selected areas in a field, coupled with the average plant stem height, is the way to detect and assess the pest before the crop is hurt. A single, well-timed application of any one of several insecticides will provide excellent leafhopper control if numbers exceed treatment guidelines. Sweep net sampling is the key to getting the timing right, before hopperburn is apparent.
Hopperburn, a V-shaped yellow area at the tips of alfalfa leaves, is the plant's distinctive response to leafhopper feeding. This results from injury to plant vascular tissue that is done as the insect feeds, and a reaction to saliva injected during feeding. In addition to lower hay quality, leafhopper damage can have a long-term impact on yield and stand persistence.
Potato leafhopper (PLH) resistant alfalfa varieties are an increasingly viable option. Newer releases show higher levels of resistance to the insect and much-improved agronomic characteristics compared to first-generation resistant lines. These PLH-varieties have an advantage over non-resistant ones if the insect is present at damaging levels. The potential is greatest during the first season while alfalfa is becoming established. There can be adequate time for leafhopper numbers to increase before the first cutting. Even if PLH-resistant alfalfa is seeded in the spring, new fields should be checked to be sure that excessive leafhopper numbers are not present.
This tiny, sap-feeding insect moves north from the Gulf States each spring on warm south winds. It shows up in established alfalfa fields during May but the date can vary from the first to the last of the month in any given year. Significant numbers of leafhoppers may find their way into spring-seeded fields in late May with rapid increase during June and a peak in early July. The leafhopper usually disappears from alfalfa fields after the July harvest.
See Insect Recommendations
for more alfalfa pest recommendations.
Infectious plant diseases in the landscape are caused by pathogenic microbes such as fungi, bacteria, phytoplasmas, and viruses. Symptoms such as wilt, leaf spot, root rot, canker, and blight resulting from microbial infections represent the plant's reaction to disease. When evidence of the pathogen such as fungal spores or mycelium, bacterial ooze, or fungal fruiting bodies can be seen, they are regarded as signs of disease. Foliar diseases of landscape plants are most noticeable and they can often be identified by symptoms seen by the unaided eye and signs visible with a hand lens.
Rust diseases.
Rust diseases often produce raised pustules on the leaf surface which produce spores which are distinctively brown, reddish brown, orange or yellow in color. Infected leaves often produce a yellow spot with pustules that are found on the undersides of infected leaves. Rust diseases are favored during wet weather with moderate temperatures. Heavily infected leaves become yellow, then turn brown and die. In Kentucky landscapes, rust can commonly be found on aster, daisy, dragonroot, geranium, hollyhock, jack-in-the-pulpit, rudbeckia, snapdragon, and sunflower. Daylily rust was found on imported plants in Kentucky a few years ago, but it does not appear to overwinter here.
Leaf spot diseases.
Leaf spots caused by fungi or bacteria are common on annuals and perennials. Symptoms vary depending on the host and the pathogen, but common leaf spot forms include angular brown or gray spots, brown spots with yellow halos, irregular blotches, tan or gray spots with reddish margins, reddish streaks and target-shaped circular spots. Some of the spots may contain tiny black pimple-like fungal fruiting structures called pycnidia. These pycnidia, as seen with a hand lens, are visible signs of disease. Spots may coalesce and blight affected leaves and heavily spotted leaves usually shrivel up and die or drop from the plant. Fungal leaf spot diseases are favored by wet, rainy seasons or frequent overhead irrigation. Examples of leaf spot of annuals and perennials include:
Downy mildew.
Yellow patches are often observed on the upper surface of leaves infected with downy mildew. On the leaf underside, the fungus produces a whitish or grayish fuzzy fungal growth consisting of sporangial stalks and sporangia, best seen in early morning while the leaves are still moist. On rose, symptoms include dark, angular spots which produce fungal signs on the leaf undersides. Infected leaves shrivel up and die. Downy mildew can be found on alyssum, ornamental tobacco, pansy, rose, salvia, and snapdragon.
Botrytis blight.
When Botrytis blight (gray mold) is active, flowers are often attacked and blighted flowers may have dead, tan spots or blotches, or turn completely brown. Botrytis also causes tan to brown leaf spots and shoot blights, especially during cloudy, cool, moist weather. When the disease is active, signs of disease appear on dead tissues as gray or tan moldy growth of the causal fungus. Under moist conditions, almost all annuals and perennials can be affected by gray mold.
Virus diseases.
Plant virus symptoms appear commonly on the foliage, but plants are typically systemically infected. Rose mosaic virus symptoms can be seen as patterns of yellow and light-green lines, splotches, or speckles on infected leaves. Yellow or brown ring spots can be one symptom of impatiens necrotic spot virus (INSV) on New Guinea impatiens. INSV and its close relative, tomato spotted wilt virus, can also cause malformed strap-shaped leaves and stunting. During recent years, unusual virus diseases of landscape perennials such as anemone, hosta, and peony have appeared in the U.K. Plant Disease Diagnostic Laboratory with symptoms of ring spots, chlorotic spots, and mottled leaves.
The 2006 Critical Use Exemption (CUE) Final Rule was signed by the EPA Administrator on January 30, 2006. These exemptions include the Quarantine and Preshipment (QPS) exemption, to eliminate quarantine pests, and the Critical Use Exemption (CUE), designed for agricultural users with no technically or economically feasible alternatives. Exemptions cover 15 crops or uses, including tomatoes, strawberries, peppers, cucurbits, orchard replants, and post-harvest uses. The request represents a continued reduction from earlier years, due to the introduction of alternatives into the marketplace and other factors.
The Final Rule, which becomes effective on February 1, authorizes about 17.6 million pounds of methyl bromide for critical uses during 2006, about 25 percent of 1991 baseline levels. The text of the rule is available at www.epa.gov/ozone/mbr
Recently diagnosed samples on fruits and vegetables have included: stinkbug damage on pecan; black knot on plum and fertilizer burn on tomato.
On turf samples we have recently diagnosed dollar spot on bentgrass, and powdery mildew on bluegrass.
On ornamentals we diagnosed cold injury, Macrophoma leaf blight and Phyllosticta leaf blight on boxwood; Phomopsis gall on forsythia; Phytophthora root rot on taxus; oedema on geranium; Gleosporium leaf spot and Rhizoctonia root rot on ivy and black root rot on holly.
UKREC-Princeton, KY, July 1-8, 2005| True Armyworm
| 18
| Corn Earworm
| 1
| European Corn Borer
| 0
| Southwestern Corn Borer
| 4
| Fall Armyworm
| 0
| | |
View Princeton trap counts for the entire 2005 season at - http://www.uky.edu/Ag/IPMPrinceton/Counts/2005trapsfp.htm
Fulton County trap counts are available at -http://ces.ca.uky.edu/fulton/anr/Insect%20Counts.htm
For information on trap counts in southern Illinois visit the Hines Report at - http://www.ipm.uiuc.edu/pubs/hines_report/comments.html The Hines Report is posted weekly by Ron Hines, Senior Research Specialist, at the University of Illinois Dixon Springs Agricultural Center.
NOTE: Trade names are used to simplify the information presented in this newsletter. No endorsement by the Cooperative Extension Service is intended, nor is criticism implied of similar products that are not named.
Lee Townsend
Extension Entomologist