Farm Ireland

Sunday 18 March 2018

Tillage advice: Recent rain was critical for crops

Oilseed rape crop
Oilseed rape crop
PJ Phelan

PJ Phelan

Last weekend's rain brought much needed moisture to spring crops. Emergence is uneven with drier areas in fields having poor ground cover and moisture retentive areas reasonably well covered in.

Areas with poor cover are a prime target for migrating aphids, which may or may not be carrying barley yellow dwarf virus.

Teagasc trials have shown yield reductions in late April sown crops of 1.1t/ha (20pc) where BYDV infection was high and 0.36t/ha (7pc) where BYDV levels were low. Best control is achieved with a single insecticide at the four-leaf stage (gs 14).

In recent years we have found resistance by aphids to pyrethoids. Currently there is no alternative insecticide so if you fail to control aphids with one insecticide on barley or oats there is no merit in going back in with a different product.

In fact doing so will increase the damage as the pyrethoids kill natural predators. This year aphid numbers are higher than normal. Aphids migrate in May when temperatures are over 15C and when there is little wind or rain present.

In coastal areas and areas with a history of high BYDV infection it is difficult to ignore the standard advice of applying an aphicide at the four-leaf stage.

However in other parts of the country strong consideration should be given to not using an aphicide and to leave natural predators do their work particularly if you get rain to coincide with the four leaf stage of the crop.

Heavy rain will drown aphids as they are washed into pore spaces in the soil which fill with rainwater. If you fail to get rain in that period or have patchy crops you may then resort to your insecticide.

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The attitude that you "may as well throw in the aphicide, as it only costs €1-€2", with your weed control makes for ease of management but is a poor decision for both environmental and insecticidal protection.

In view of the fact that we are relying on research that is more than 10 years old for our current recommendations and the advent of aphid resistance there is a need for further research and assessment of the impact of current practices on predator populations.

Last weekend's rain came just as some farmers were considering applying liquid feeds/trace elements to help struggling crops. The benefit of such is questionable unless you have identified specific deficiencies.

You will not grow a field crop with liquids unless you have a fortune to spend. That said manganese deficiency has shown up in many winter barley crops and it is most likely that responses will be got from foliar manganese applications. Seed treatment with manganese is effective for spring crops in fields with a history of managanese deficiency.

Seed treatment of foliar zinc is essential in areas on known zinc deficiency. Copper deficiency is normally confined to organic soils. Magnesium deficiency is frequently seen when crops are under moisture stress.

N16 is a foliar N fertilizer containing 16pc N 2.5pc Mg and calcium (facilitates uptake). Manganese and other trace minerals can be added to the formulation.

Application rate is typically 20 to 30 l /ha. It is claimed that the N is four to six times more effective than soil applied products. Many farmers have found that application to cereals with the final fungicide usually results in larger grain, higher bushel and slightly higher protein level.

All wheat crops have septoria on the lower leaves. The dry weather up to now kept that at bay. However heavy rain over the past few days will have caused splashing which will have carried spores up on to the higher leaves.

Crops that got their T1 fungicide in early May should be well covered for that. However crops that got their T1 mid to late April will now have very little fungicide protection. It is too early for the T2 which should not take place until the flag leaf is emerged. Consideration should be given to a T 1.5 - perhaps simply chlorothanonil on its own or if the pressure is higher something with a bit more firepower. Discuss with your agronomist.

Emergence of spring oilseed rape has been very uneven making it very difficult to get the timing of an aphicide right. Crops currently range from some seed still germinating to others at four true leaves. Peak risk is from emergence to full cotyledon.

Harsh winds have helped to minimise damage but a short period of calm weather and bright sunshine can see a lot of damage. Inspect crops daily and spray if damage is evident in more than 25pc of the seedling at the susceptible stage.

PJ Phelan is a tillage advisor based in Tipperary and is a member of the ACA and ITCA

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