Supplemental Label for Headline Fungicide for “Plant Health”

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Headline and other related fungicides called strobilurins including Quilt, Quadris and Stratego have been applied extensively in the US in last few years to enhance yields of corn, soybeans and wheat. Locally, the majority of the use has been on field corn in irrigated high yield environments. The “Plant Health” claims in this new supplemental Headline® label initiated a vigorous discussion among Extension Plant Pathologists throughout the East and Mid-West concerning the claims on this new label. The following article addresses those concerns from a scientific, unbiased perspective of the authors. This is a thoughtful and well articulated article and I am sure this is not going to be the last word on this topic but it explains the issue and the concerns pretty well.

Supplemental Label for Headline® Fungicde for “Plant Health”: Will It Improve Corn, Soybean and Small Grain Health?
By Paul Vincelli, Don Hershman, and Chad Lee*
Departments of Plant Pathology and *Plant and Soil Sciences
Kentucky Pest News, Number 1187, February 24, 2009, online at: www.uky.edu/Agriculture/kpn/kpnhome.htm

A couple of weeks ago, we learned of a supplemental label for Headline® fungicide for use on several crops for “disease control and plant health.” The impacted crops grown in Kentucky are corn, small grains (barley, rye and wheat), and soybean, as well as other edible legumes. Headline® and related strobilurin fungicides (Quadris®, Quilt®, and Stratego®) provide excellent control of certain fungal diseases of the above crops. In Kentucky, for example, use of these products to control gray leaf spot and/or northern leaf blight in corn, frogeye leaf spot and brown spot of soybean, and tan spot and leaf rust of wheat makes sense when the risk of disease is high. However, this new supplemental label makes claims that go way beyond disease control.

Claims Made on the New Supplemental Label
The supplemental label indicates that, through preventive applications of Headline® to crops, the plant health benefits may include improved host plant tolerance to yield-robbing environmental stresses, such as drought, heat, cold temperatures, and ozone damage. The supplemental label also claims that Headline can improve plant utilization of nitrogen and can increase tolerance to bacterial and viral infections. These benefits often translate to healthier plants producing greater yields at harvest, especially under stressful conditions. The supplemental label also claims that additional specific benefits can occur, including:

● Improved stalk or straw strength and better harvestability (barley, corn, rye, wheat)
● Induced tolerance to stalk diseases (corn)
● Better tolerance to hail (corn)
● More uniform seed size (corn, soybean, and edible legumes)
● Better seed quality (soybean and edible legumes)

Will “Plant Health” Be Improved?
Based on publicly available research reports, we see very little evidence that Headline® or other strobilurin fungicides should be applied to any of the above crops for any reason other than disease control. To date, no data have been circulated in either the scientific or farm communities which suggest that any strobilurin product, including Headline®, can reliably live up to the claims made for stress tolerance under field conditions.

Claims of stress tolerance sound exciting but, based on the data we have seen, deserve to be viewed with cautious skepticism. There are certainly studies in the laboratory, the greenhouse, and occasionally in the field that show beneficial physiological changes in crops treated with strobilurin fungicides. But don’t assume that the beneficial changes observed in those studies result in increased yield under field conditions. When a greening effect and/or yield improvement is observed in a treated crop (in the absence of significant disease pressure), it is assumed that stress tolerance and/or improved plant health (apart from disease control) is at work. This isn’t necessarily true. In order for any real-world stress tolerance claims to pass muster, scientifically, it is necessary to conduct replicated field studies where the appropriate environment, plant, and crop measurements are made, and appropriate experimental controls are in place. We do not believe these data exist in sufficient quantity to support the above stress tolerance claims. Certainly, it is inappropriate to draw conclusions about stress tolerance based solely on crop appearance and yield. For example, we have observed the greening effect in field crops, but it often does not translate to higher yields. We have also observed occasional yield increases in crops (mostly soybean) following a fungicide application, when no obvious disease symptoms were present. But there are a large number of potential reasons why yields are improved in treated crops. Tolerance to one or more stresses is a possibility, but it is also possible that some soil-borne disease or disease complex is being controlled, but we cannot easily observe it. There are many other possible reasons and the only way to know for certain is to conduct the appropriate replicated, controlled field studies.

Let us look at an example from soybean from two replicated studies conducted at the Research and Education Center where disease pressure was minimal and late season moisture stress was significant (especially in 2007). If Headline® application improves tolerance to drought stress (as per the supplemental label), then the application should improve yield in treated crops. But as can be seen in Table 1, soybean yields were not improved by Headline® in either year. Table 2 shows the results of a similar field trial for corn conducted on a Kentucky farm under drought conditions. You can see that Headline® provided no yield bump.

Table 1. Results of Headline® application (6 fl oz + Induce at R3 stage) in soybean where disease pressure was insignificant, under late season moisture stress (UKREC, Princeton, KY, 2007-2008)

Treatment

2007
Yield (bu/A)

2008
Yield (bu/A)

Check 24.5 51.5
Headline 23.8 53.0
Statistical result (LSD, P=.05) No statistical difference No statistical difference

Table 2. Results of Headline® application in corn where disease pressure was insignificant, under late-season moisture stress (Logan County, KY, 2007)

Treatment

% Gray Leaf Spot*

Yield (bu/A)

Check 1.3 160
Headline 2.0 155
Statistical result (LSD, P=.05) No statistical difference No statistical difference

*Disease assessed on ear leaf at half milk line.

It is important to emphasize that the data in Tables 1 and 2 are merely examples. The above data are typical of what has been seen over and over in a large number of university-conducted trials conducted over the past several years in corn, soybean, and small grains. If Headline® regularly improves yields by imparting stress tolerance to crops in the absence of disease, then more complete and convincing proof needs to be made public. And in the world of science, claims based on evidence that has not been made public are treated with suspicion.

The claims about improved stalk health in corn are not unreasonable. Occasionally (and we stress the word occasionally), applications of strobilurin fungicides have been shown to improve stalk strength and/or reduce stalk rots in university-conducted field trials. However, in our experience, that improvement in stalk health relates to control of foliar diseases (gray leaf spot, for example). You see, if foliar diseases are aggressively attacking the plant during grain fill, then the corn plant will attempt to fill the grain by cannibalizing the reserves in its own stalk. That weakens the stalk and can result in more aggressive stalk rots as well as reduced stalk strength. So, if foliar diseases are killing the upper and middle foliage during grain-fill, then it makes sense that a fungicide like Headline® might sometimes improve stalk health, which it sometimes does. But note carefully: this benefit still relates to control of foliar diseases. And like we said above, strobilurin fungicides are very good for controlling foliar diseases like gray leaf spot and northern leaf blight of corn if these diseases are present.

What about a fungicide enhancing tolerance to hail? Actually, conducting a study that tests for this type of benefit is more complex than you may realize. You must have the right kind of experimental design or you could be misled by the results. The only study we are aware of that tests this claim with a valid experimental design is one conducted in 2008 by Dr. Carl Bradley and colleagues at the University of Illinois. In that study, researchers used a weed-eater to simulate hail damage. In that study, they found absolutely no yield benefit from Headline®, Quadris® or Quilt® when applied following simulated hail damage.

Is There a Downside?
Producers should be aware that sometimes the late-season “greening” effect observed with strobilurin fungicides can result in higher grain moisture and therefore additional drying costs and a slower (more expensive) harvest. Conversely, if crop harvest is delayed until the desired harvest moisture content is reached, there can be a yield and/or quality penalty, depending on the crop. For example, delaying wheat harvest will result in delayed planting of doublecrop soybean, which can lead to lower yields in soybean. In soybean, if harvest is delayed, pod and stem blight levels may increase, which can reduce the quality of grain destined for seed use. This may necessitate additional grain clean-out and/or the use of seed-treatment fungicides prior to planting next season. (Strobilurins, in general, do not do a good job in controlling soybean pod and stem blight). The bottom line is that fungicides applied to corn, soybean, and wheat will sometimes increase production costs.

Another concern specifically relating to the plant health issue is that the use of a fungicide when disease activity is too low to affect yield increases the risk of fungicide resistance. It is because anytime you expose a fungus to the fungicide, even when fungal activity is low, you increase the selection pressure on the fungus towards resistance. Resistance to strobilurin fungicides is an important concern worldwide, and the use of any strobilurin fungicide for plant health reasons increases the risk of developing strobilurin-resistant gray leaf spot. Use of strobilurins may also incite flares in certain insect and mite populations under field conditions, because fungicides can sometimes suppress fungi that kill these arthropod pests.

Bottom Line
The strobilurin fungicides are very good for control of specific crop diseases (see product labels for a list), if they are present at high enough levels (or the risk is high enough) to reduce yields. However, applying a strobilurin fungicide for plant health or stress tolerance reasons alone – with little or no threat from foliar diseases – doesn’t make sense to us, based on our extensive study of the best available information. Land-Grant University trials, thus far, generally do not support claims of reliable improvement in crop yield under stress conditions from an application of Headline®, or any other strobilurin fungicide. Nor have fungicide manufacturers provided sufficient field evidence in support of these claims. In fact, the vast majority of industry data show yield impacts (usually in side by side comparisons) associated with specific fungicide treatments, but provide no measurements of diseases or stresses. The upshot of this is that there is absolutely no way to know what the cause of apparent yield improvement is in the vast majority of industry studies. Thus, at this time, we do not feel there is a scientifically defensible basis for assertions of improved plant health/stress tolerance in the absence of the diseases the fungicide was originally developed to control.

Seed Quality Issues Lead to Reduced Stands

Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

I have looked at sweet corn, soybean, and lima bean fields recently with reduced stands and low vigor plants due to poor seed quality. It is often assumed that summer plantings will not have stand issues as soil temperatures are warm and seeds should germinate and emerge quickly (if there is adequate moisture). This is not always the case, especially if seed lots are of low vigor. Signs of low vigor seed will be: abnormal appearance in the bag (shrivelled, cracked, off color, misshapen); small seedlings that emerge late or do not emerge at all; abnormal growth (twisting, snaking, or corkscrewing); small shriveled cotyledons in beans; small or distorted true leaves; swollen or split hypocotyls or coleoptiles; and bleached out seedlings. Another issue affecting seed germination and emergence would be uneven or inadequately applied seed treatments (fungicides and insecticides).

The following are some pictures of a summer lima bean planting with reduced stands due to poor seed quality.

 

Low vigor lima bean seedling – note the stunted and white appearance

 

Abnormal lima bean seedling with distorted leaves

 

 Uneven and reduced lima bean stand due to poor seed quality

Uniformity in Processing Vegetable Crops

Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

Pea harvest will begin at the end of May; the first pickles have been planted; early plantings of sweet corn and snap beans are in the ground; lima bean planting will begin at the end of the month. A key to profitability in these processing vegetables is having a high percent of the crop at peak when harvest begins. Wide variability in crop maturity will lead to significant quality discounts. To achieve maximum returns and highest quality, the crop should be as uniform as possible. The following are considerations in achieving uniform crops:

1. Choose your most uniform fields to plant processing vegetables. Wide variations in soil conditions will lead to differences in crop growth, development, and maturation. Early plantings should be in fields that warm up evenly, with few, if any, low spots and wet areas. Avoid planting in fields that are prone to crusting. Avoid fields with shading from woods or hedgerows.

2. Tillage operations should be performed as to produce a seedbed that will allow for good seed to soil contact and rapid seed emergence. If soils are dry, irrigate to raise moisture levels prior to seedbed preparation. Make an effort to deal with compaction prior to planting. Variability in field compaction is one of the primary causes for non-uniformity in processing vegetables. Manage field traffic prior to and after planting to avoid additional compaction.

3. Planting operations are critical. Use planters that will deliver seed precisely with uniform spacing and depth. The goal is to have the crop all emerge at once. Late emerging plants will be much less productive and will be behind in maturity. This is particularly important for processing sweet corn. Change planting depth to account for soil conditions (moisture and temperature).

4. Plant entire field sections that are to be harvested together on the same day. Large differences in maturity have been seen in delays of just one day. In spring plantings, plant when a warming trend is predicted. Avoid planting if heavy rains are forecast. Avoid planting in wet soils and in conditions unfavorable to germination and emergence. Do not plant when soil temperatures are below critical values for that crop.

5. Use high quality seed. Seed should be of high vigor and high germination percentage. Handle seed gently so as to preserve quality. This is particularly important with beans.

6. Pay attention to seed protectant chemical choices and adjust seed or furrow/banded applied fungicides and insecticides to match fields and planting dates.

7. Work with processors to match varieties for the planting date as much as possible. Early plantings should be made with cold tolerant varieties. Late plantings should be planted with varieties that can tolerate heat during maturation. Split sets are a particular problem in crops exposed to stress conditions, especially heat and/or water stress.

8. Plant at recommended populations. The interaction of plant density with emergence and germination rate can have a significant effect on uniformity at harvest.

9. Manage irrigation so that water is applied as uniformly as possible. Center pivots and linear move systems are preferred over traveling guns. Have irrigation systems checked for uniformity. Money spent on replacing bad nozzles will be rewarded with more uniform crops. Use irrigation as tool to achieve even emergence in dry conditions and to “soften” crusted soils.

10. Pay attention to soil fertility variations. Processing vegetables will benefit from fields that have been grid sampled, particularly to manage soil pH. Many fields have wide variations in pH and variable rate liming can help to achieve a more uniform crop.

11. Apply all inputs as evenly as possible. This includes fertilizers, fungicides, insecticides, and herbicides. Check fertilizer application equipment, especially starter fertilizer applicators and sidedressing equipment for uniformity.

12. Avoid the use of pesticides that may cause damage to the crop. In particular, herbicides should be used with care. Non-uniform application or incorporation of preemergence herbicides will lead to variable crop emergence; damage by post-emergence herbicides will lead to more variable crops.

13. Weed control is an important part of achieving uniform crops. Map weed populations in fields and target controls to take into account higher weed density areas, or areas with particularly troublesome weeds (spot spraying, hand work or extra cultivation may be necessary in these areas).

14. Cultivation practices should be done at a uniform depth and distance from the row. It is best to use one operator for a given field. Train operators on how to cultivate in a proper manner. Adjust cultivators for differences in soil conditions. Excessive root pruning during cultivation can lead to delays in maturity, additional stress on the crops, and increase the risk of split sets.

A Review of Sweet Corn Types and Isolation Requirements

Emmalea Ernest, Extension Associate, Vegetable Crops; emmalea@udel.edu

Half of the genes expressed in a kernel of corn come from the plant producing the ear and half come from the pollen grain that fertilized the kernel. The expression of the pollen genes in the seed makes it necessary to isolate sweet corn from field corn, pop corn, and, in certain cases, from other types of sweet corn. The genes that make sweet corn sweet are all recessive, which means that a kernel of sweet corn must have two copies of the gene (one from the mother plant and one from the pollen parent) in order for the sweetness trait to be expressed. (See Table 1 for a listing of the genes discussed in this article.) Field corn and pop corn carry the dominant starch producing forms of these genes. Consequently, if field corn or pop corn pollinates sweet corn, the starch producing genes from the field or pop corn will be expressed instead of the genes from the sweet corn. Understanding why certain types of sweet corn must be isolated from one another is a bit more complicated.

Table 1. Recessive Sweet Corn Genes and Their Dominant Counterparts

Gene Description
Su-1 Dominant starch-producing gene
su-1 Recessive sugary gene
Se Dominant starch-producing gene
se Recessive sugary enhancer gene
Sh2 Dominant starch-producing gene
sh2 Recessive shrunken-2 gene

There are two sweet corn isolation groups which can be further broken down into six basic categories and then nine different genotypes. The following is a discussion of the six categories accompanied by Table 2 which details the nine different genotypes available, their advantages, disadvantages, and isolation groups.

Normal
Normal sweet corn varieties, such as Silver Queen, carry the sugary gene, su-1. The sugary gene increases the amount of sugar in the developing ear. However, the disadvantage of the normal sweet corn varieties is that the sugar is quickly converted to bland-tasting starch after harvest. This is the sweet corn that needs to go directly from the field into a pot of boiling water.

Sugary Enhanced
The sugary enhancer gene, se, works in conjunction with su-1. The se gene increases the amount of sugar produced in the kernel and also increases the tenderness of the kernel. Some sweet corn hybrids are heterozygous for se. This means that the hybrid carries only one copy of se. Consequently the ears produced by a heterozygous se hybrid have approximately 75% normal sweet corn kernels, and about 25% sugary enhanced kernels. Homozygous se hybrids carry two copies of se, which results in ears with 100% sugary enhanced kernels. Sugary enhanced varieties start out with more sugar in the kernels so they stay sweeter longer (up to a week at 32 – 34°F). However, the sugars will eventually be converted to starch. Some people like the tender, creamy texture of sugary enhanced corn while others would term it mushy.


Silver King – a homozygous sugary enhanced hybrid

Supersweet
Supersweet sweet corn varieties carry the shrunken-2 (sh2) gene. This gene causes very slow conversion of sugar into starch. Consequently, hybrids that carry sh2 maintain their sweetness for a long time, up to 21 days when cooled to 32 – 34°F. The kernels of supersweet corn are described as crisp by fans and tough and watery by detractors. Because even the mature kernels of supersweet corn do not contain much starch, plantings are more difficult to establish. Seed should be handled with care and soil conditions should be as close to optimum as possible (soil temperature at least 60°F and adequate but not excessive moisture).

Some supersweet varieties do not carry su-1. Instead they have the dominant form of the gene, Su-1. If supersweet hybrids are pollinated by normal or sugary enhanced sweet corn the combined effects of Su-1 from the supersweet and Sh2 from the normal or sugary enhanced hybrids will produce starchy field corn-like kernels. This is why supersweet hybrids must be isolated from normal and sugary enhanced hybrids.

Synergistic
Synergistic sweet corn hybrids carry su-1, one or two copies of se, and one copy of sh2. The combination of the effects of the se gene and sh2 results in tender kernels with very high sugar content. Synergistic hybrids produce ears with a mixture of kernel types. The ratio and types of kernels produced depends on whether the hybrid has one or two copies of se (see the table for details). Because they carry the dominant Sh2 gene, synergistic sweet corn varieties should be isolated from supersweet varieties. A few synergistic varieties have the brittle-2 (bt2) gene instead of sh2. The bt2 gene’s effect on kernel sweetness is about the same as the effect of sh2 and both genes work in nearly the same way. Synergistic hybrids have the advantage of similar seed vigor to the normal and sugary enhanced hybrids.


Misquamicut – a synergistic hybrid

Augmented Shrunken
Augmented shrunken or “augmented supersweet” hybrids carry Su-1, two copies of se, and two copies of sh2. The ears produced by augmented hybrids have 100% tender supersweet kernels, which, due to the combined effects of se and sh2, are tenderer than regular supersweet corn. The tender supersweet kernels are appreciated by some, but others prefer the crunchy texture of the supersweet hybrids. Augmented shrunken varieties must be carefully hand harvested because their very tender kernels will be damaged by machine picking. Augmented varieties need to be isolated from normal, sugary enhanced and synergistic hybrids. Additionally, they have the same seed vigor problems as supersweet varieties and should only be planted under optimal conditions.

Xtra-Tender 377A – an augmented shrunken hybrid

MiraiTM
MiraiTM sweet corn varieties carry two copies of all three sweet corn genes: su-1, se and sh2. They have all tender supersweet kernels and, like the augmented shrunken varieties, need to be hand-harvested. MiraiTM varieties also need optimal soil conditions for seedling establishment. MiraiTM does not require isolation to avoid starchy kernels, but, like all of the sweet corn types, isolation from other sweet corn types is necessary for the best quality.

View Table 2. A Comparison of Sweet Corn Genotypes here.