Weather slows wheat disease

IT IS still raining and unsettled; applying crucial sprays like T2 fungicides and first blight sprays has been frustrating. Hopefully, by the time you are reading this, the sun will be shining. If it is, what are you doing inside?

Most wheat crops now have the flag leaf fully emerged, and about two-thirds are in boot. The most forward crops of Rialto, Charger and Soissons have ears emerging. The cool wet weather has slowed disease spread, as well as spraying activity, with yellow rust making little progress.

If you have not already sprayed the now fully-emerged flag leaf, it is vital to do so as soon as possible. Waiting for ear emergence is a mistake which only allows disease to develop on the upper leaves and reduce their ability to fill the grain. (Landmark and Mantra or Amistar, Twist mixed with a good triazole such as Opus will give the best results in a period of such high disease pressure).

Although cereal aphids continue to be found in small numbers in many winter wheat crops, populations have shown few signs of increasing rapidly during the cool, wet weather. Warmer conditions are now forecast and this is likely to increase migration pressure into crops, as more wheat crops reach the ear emergence stages. We have seen no crops in which thresholds for aphid control have been reached.

Winter barley now has ears fully emerged and is flowering. Some crops have grown tall, due to late nitrogen and wet weather, and are starting to lodge.

A slightly higher percentage of crops have had their T2 sprays than in wheat, and in some cases a late T1 became a timely T2! Rhynchosporium remains the main disease problem, and where the T1/T2 was applied early, it is possible that there could be further development. Brown rust is often present but at low levels and, with warmer weather, may increase after flowering, as it did in some areas last year. Monitor crops and apply further treatments if disease pressure increases.

Spring barley crops are more backward than last year, and late-sown crops have been doubly hit by the weather in both April and May. Although potentially a low input crop, both rhynchosporium and mildew have produced quite high early infection levels in some crops of Optic. Chariot generally has rhynchosporium but far lower levels of mildew.

Oilseed rape crops are at or close to the end of flowering and seed is at the translucent stage. Heavy rain has caused some lodging problems in a few tall crops but most are standing well. Spring oilseed rape crops vary, from crops still struggling to establish with only 2-3 true leaves up to well-established plants with flower buds visible, depending on seedbed conditions and when crops were sown. The most forward crops have reached the green to yellow bud stages and are becoming susceptible to pollen beetle damage, check now! Do not forget grassweed control - wild oats can provide a nasty shock as they emerge through the pod canopy. There are many graminicide options such as Fusilade, Falcon and Laser.

Chocolate spot rust and downy mildew have all increased in winter beans during the last week. Chorothalonil will provide protection against but not contain established rust. Adding a rust specific product is the preferred option for overall control. Folicur is recommended for chocolate spot and rust.

Potato planting has now been completed and growth stages range from crops yet to emerge to forward maincrops at around 40pc ground cover and meeting along the rows. Blight has already been seen in the area on dumps, so effective programmes are vital. Always stick to recommended spray intervals.

Hopefully, by next month, the sun will be shining and we can look ahead to varieties for next year.

This column is supplied by Derek Knight 01430 861988 and Julie Cartner 01904 491478 who are consultants for ADAS in East and North Yorkshire.