'Clean' crops could be masking high levels of disease
Published 20/05/2015 | 02:30
Crop growth stages and spray programmes are extremely variable, so farmers have had to take every chance and half chance to spray.
However, early morning spraying onto wet crops is not a solution. And don't be fooled into thinking that you can get away without spraying. Low temperatures has slowed disease development so that many crops appear to be clean now, even thought they may actually be carrying high levels of disease.
T1 sprays on winter wheat started at the end April, and many only managed to finish up last week as the second leaf was emerging. Low temperatures are also slowing leaf emergence. Leaf development requires 120 day degrees, so it will take 12 days at an average temperature of 10C. Crops with the second leaf fully emerged now are therefore 12 days away from full flag leaf. That is your timimg for the T2 regardless of spray interval.
If your interval is going to be longer than 3 weeks, you should apply a T1.5 with chlorothanonil. If the interval is short go, you should spray anyway as this is the last chance you have to get good systemic activity with your fungicide. Later applications will give reduced activity and increase disease risk. Remember that a well timed T2 can give you a 50pc yield response.
Make sure to use a product with strong septoria eradicant activity. Where disease pressure is high look to products containing Fluxapyroxad and epoxicinazole or prothioconazole and bixafen. Don't rely on products with a single active ingredient unless the tank is mixed with an appropriate partner. This is certainly not a year for using reduced product rates. If you were one of the people that paid ridiculous money for conacre, you can't complain about price of fungicides either.
The final spray on winter barley should be completed within the next few days. It should be timed after awn emergence and before the head is fully visable. Application after the head is fully emerged gives a poorer yield response. Use a mix containing prothioconazole or cyprodinil and SDHI or a strobilurin.
Winter oats look good, with the main risk now either mildew or rust. Mildew can be prevented with the use of proquinazid. A strobilurin and morpholine will prevent rust and knock mildew. Check labels to ensure product approval for crops before application. Note chlorothanonil is not approved on oats.
If spraying is on land with water courses or even dry open drains you must adhere strictly to the specified buffer zones.