Four reasons not to mix an insecticide with nitrogen
Recent research from North Carolina has suggested that there are times where tank mixing an insecticide with your nitrogen can be cheaper than using scouting and thresholds for cereal leaf beetle. The biggest reason for this is because there is a yield penalty for driving over wheat after jointing and because scouting costs money. However, there are a number of reasons why I do not recommend this for 2014.
1. When wheat is $6 per bushel, you can save on average $2 an acre using the tank mix approach. However, when wheat is $4 a bushel, you lose $2 an acre using the tank mix approach. This includes the cost of paying a scout, as well as the yield penatly incurred from drive down over the wheat. You can save even more money by doing the scouting yourself (a simple trip to the field in mid-April is better than nothing!) or by applying by airplane if needed (something you may want to do anyway if it continues to remain wet).
2. Cereal leaf beetle tend to be worse in thin stands. Contrary to common opinion, this is not because cereal leaf beetle prefer thin wheat (they actually prefer thick and healthy wheat), but because there are simply more beetles per tiller in thin stands compared to thick ones. We have a lot of thin wheat this year and cereal leaf beetle could be more of a problem than in the recent past.
3. Cereal leaf beetle doesn’t leave overwintering sites until daily high temperatures are consistently above around 60 degrees F. This means that on following a cold winter/spring, we might expect cereal leaf beetle to take longer to leave overwintering. NCCE recommendations are to apply nitrogen before the middle of March and before jointing. This means your insecticide will be applied much to early to do any good against the beetle if you tank mix with much-needed nitrogen over your field.
4. Even in a good year, you can still lose to cereal leaf beetle. Although, on average, you can save by tank mixing when wheat prices are $6 a bushel and higher, cereal leaf beetle can still overwhelm your field if they invade in high densities. The residual of the insecticide runs out after a month. Hence, the tank mixing approach is much riskier than scouting and using thresholds.
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