Keeping up with changing crop technology can be a full-time job. Jeremy Veach, technical sales agronomist with DuPont Crop Protection in southeast Iowa says, “Growers get inundated with information which complicates planning. It’s my job to wade through all of that information to help my growers develop solid crop management programs.” Veach answers common questions to help guide your decision-making in 2017.
1. How do I know if I have herbicide-resistant weeds?
It’s not easy to identify herbicide-resistant weeds based on field observations alone. If a herbicide fails to control a weed that is normally susceptible to the rate of herbicide you applied, you may have a resistant weed population, especially if adjacent weeds are effectively controlled. To confirm resistance, submit suspect weed samples for testing. Purdue University offers testing on seeds or leaves of waterhemp, Palmer amaranth and giant ragweed for resistance to ALS, glyphosate and PPO herbicides.
In Iowa, glyphostate-resistant giant ragweed, marestail and waterhemp populations have been documented. Palmer amaranth, which has developed herbicide resistance in the southern U.S., is gaining traction in Iowa fields. Before this summer, Palmer amaranth had only been identified in five Iowa counties; this year the weed was found in 16 counties. No resistance has been documented in these Palmer amaranth populations, but experts are concerned because of the weed’s ability to quickly adapt to herbicide programs.
While resistant weed populations are increasing, many herbicide failures are due to factors other than resistance. Application factors, including time of day, environmental conditions, application practices and insufficient herbicide coverage can all contribute to herbicide failure.
2. How can I reduce the spread of resistant weed populations?
Get into the habit of using best management practices to help control the spread of resistant weeds. Scout fields early and regularly throughout the season and take note of weed species. Herbicides are most effective when weeds are small and growing quickly, so a timely application is important. If appropriate, a post harvest burndown herbicide application to control winter annual weeds will help ensure fields are clean for planting.
Diversifying your herbicide strategy makes it more difficult for weeds to develop resistance. Use multiple modes of action and tank-mix grass and broadleaf herbicides for broad-spectrum weed control.
Layering residual herbicides extends the period of weed control. A study by the University of Minnesota reported that control of glyphosate-resistant waterhemp dropped sharply by late June when using a preemergence herbicide alone. In contrast, layering a preemergence herbicide with a residual postemergence application provided 90 to 95% control of glyphosate-resistant waterhemp through September. Always use full application rates and follow label instructions for effective weed control.
Preventive and cultural practices, such as keeping ditches and field borders free of weeds, cleaning harvest and tillage equipment between fields, rotating crops, and planting in narrow rows to increase crop competition, can all help control the spread of resistant weed populations.
3. Do I need to use fungicides?
Agronomists get this question every year, and the answer depends on the season. The short answer is that you should use a fungicide if disease pressure is high enough to reduce yields. To help you make the decision, take into account disease severity, number of plants infected, future weather conditions expected, and how susceptible your hybrids and varieties are to disease. Scouting for disease early and often can help you stay ahead of disease progression and time your fungicide application for the maximum return on investment.
Iowa Soybean Association On-Farm Network trials over a nine-year period showed that corn yields increased an average of 5.2 bushels per acre after a fungicide application. During high disease years, the average increase rose to 8.4 bushels per acre.
Fungicide applications also help maintain stalk integrity late in the season. When plants are stressed by disease, photosynthesis and sugar production are reduced. To continue filling grain, the plant compensates by remobilizing sugars from the stalk. That is why stalks sometimes become soft late in the season during grain fill. When weather delays harvest, a mid-season fungicide application can help ensure your crop will still be standing when you’re able to run the combine. Growers who saw corn standability issues this year could benefit from a fungicide application if choosing similar hybrids next year.
4. What will disease pressure be like next season?
While it’s hard to predict what kind of diseases the season will bring, there are clues that can help you prepare. Most growers know that many diseases, particularly fungal pathogens, overwinter in soil.
Growers often believe a cold winter will mean less disease next year, but that isn’t necessarily true. Fungal spores have evolved to adapt to harsh conditions. They can be insulated by soil, plant residue and snow, allowing them to survive extreme winter temperatures. Don’t rely solely on winter conditions to set expectations for disease pressure next year.
The best indication of what disease pressure might be like next season is to review field history, cultural practices, and hybrid and variety choices. These factors, combined with in-season weather conditions, are better indicators of what you can expect for disease pressure the following season.
Areas of Iowa saw heavy rains late in the season, leading to fungal diseases like northern corn leaf blight and gray leaf spot. Poor late-season stalk health was also a problem, especially in areas where harvest was delayed. Watching fields for disease in 2017 will be important, especially if we get another wet year.
Diseases thrive in fields with reduced tillage and no crop rotation. Reduce plant residue in fields, manage weeds and rotate crops to help reduce disease problems. Find disease management strategies here.
Scout fields throughout the season for signs of disease, since environmental conditions and disease pressure can change quickly. Insects are also vectors for disease, so controlling them can help reduce disease. Be prepared to apply fungicides if diseases like gray leaf spot or northern corn leaf blight threaten yields. DuPont Aproach® Prima fungicide delivers two modes of action for effective disease control in corn and soybeans.
5. How can I get the most from my input dollars?
Understand your fields and identify the main trouble areas you need to address. Every grower has different input needs and costs. Consult with your trusted agronomic advisor to help you make input decisions.
Choose suppliers who allow you to buy chemical and seed products early to bundle savings. You’ll also benefit by matching your seed genetics with the appropriate crop protection program. The DuPont™ TruChoice® Early Pay Multiplier program allows you to multiply your savings upfront for the purchase of seed and crop protection products.
One area where you shouldn’t cut corners is weed control. You’ll likely end up paying more in the long run with reduced yields and less harvest efficiency.
If your equipment is set up with precision agriculture technology, use it. Work with your agronomist to develop a prescription for planting populations and fertilizer and crop protection applications. This allows you to focus input dollars on the acres that have the highest potential for top-end yield.
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