Seeing more and more of two things in my area- tassels and aerial applicators (planes and choppers). Fungicide application season is upon us.
In talking with growers and retailers the last few weeks, this is shaping up to be a big year for fungicide apps, so just a few thoughts for guys “on the fence” and trying to decide to spray or not.
In soybeans, we are still pretty early, not much disease pressure yet; and we are a little ways off from late R2/R3 when we typically want to see the fungicides go on, so keep scouting the beans for diseases and other pests like aphids, Japanese beetles, etc to be sure they aren’t a problem yet (we haven’t seen much activity over here with bugs either); if things look good, delay applications until later.
In corn, we pretty much know the drill-
Most everyone agrees that the number-one factor impacting fungicide application profitability is management of common diseases (gray leaf spot, common rust, etc.). If crop diseases are present, yield responses to applications are typically higher on hybrids that have low disease resistance scores. If disease levels are high enough, hybrids with solid disease resistance may respond well, too.
Warm, humid conditions around grain fill favor the development of diseases. Crop history and crop residue levels can contribute, too. With several pathogens that survive in corn residue, corn-on-corn and other high-residue systems can increase disease levels. Geography can also influence disease. For example, southeastern Iowa tends to be warmer and more humid than much of the state and historically has had higher levels of diseases. While sometimes we see fungicide applications increase yields in fields with low disease pressure, increasing disease pressure is a better indicator to the potential profitability of treating.
Application timing can influence the odds of a positive return. Combining label recommendations and field observations is critical. If applied too early, the residual effects of the product may be gone as diseases set in. If applied too late, it may not effectively control the diseases already established. Most agronomists agree that the full tassel stage (VT) through blister stage (R2) is the optimum timing if a fungicide is needed. We are just now getting there in this part of the Iowa.
Scout hybrids with moderate to low disease resistance more intensively.
Scout more often if the weather’s warm and humid and if rainy weather is present or predicted for July and August.
Watch corn-on-corn, high-residue fields closely.
Late-planted corn often is more susceptible to diseases.
Don’t cut product rates.
Fungicide Apps- Ground vs Air
Of course in corn most are done by air, but in beans guys have more flexibility with ground rigs. So wheel traffic impact on bean yields is a common question we get. Purdue has a tech sheet that talks about the issue- they put it together including Iowa data with help from our own Mark Hanna; wheel track damage made from ground applications can impact soybean yields. Sprayer wheel traffic from first flower (R1) through harvest can damage soybean plants and reduce yield (Hanna et al. 2008). Our research suggests that an adequate soybean stand (more than 100,000 plants per acre) planted in late April through mid-May can compensate for wheel tracks made when a field is sprayed at R1. Yield loss can occur, however, when wheel tracks are made at R1 or later in thin soybean stands (less than 100,000 plants per acre) or late planted soybeans. Regardless of stand, plants could not compensate for wheel tracks made at R3 (early pod development) or R5 (early seed development). The average yield loss per acre is based on sprayer boom width (distance between wheel track passes). In our trials yield losses averaged 2.5, 1.9, and 1.3% when sprayer boom widths measured 60, 90, and 120 foot, respectively. Multiple trips along the same wheel tracks did not increase yield loss over the first trip.
So, to address the “ground vs air” on the product performance side of things… research in the Midwest is limited. Some good work done by ISA work on corn showed only a .2 bushel per acre difference between ground vs air. Experience tells us that both can be very effective on insect and disease pests in corn and soybean fields; operator/pilot skill and ensuring the right spray parameters for each type of application is a big player in how well the pesticides will work. Bottom line is that pick the method that fits your operation the best, both are good options.