PGRO CROP UPDATE No7: 4th August 2015

Combining pea desiccation
If you are considering desiccating combining peas with diquat the correct stage of application is important. Moisture content should be between 40-45% when the crop is turning yellow, bottom pods are parchment-like and the seed is hard. Middle pods should be pitted and crinkled, pods becoming parchment-like with rubbery seeds within. Top pods will still be fleshy and green/yellow. If peas are for human consumption please consult your processor before using any wetter with diquat.

If desiccation takes place too early when insufficient lignification has taken place the haulm can collapse, the crop lodges and yield may be affected.

Intervals between desiccation and harvest will vary depending upon the weather. Following applications of diquat, crops are usually ready for combining 7 – 10 days later. Glyphosate is available pre-harvest to control excessive green weed growth but work at PGRO has shown it has little desiccant action in peas. Generally at least 7 days should elapse between application and harvest and average moisture content before application should be below 30%. Pre-harvest glyphosate should not be used on seed crops. For further information see PGRO technical update number 27.

Field bean desiccation
As well as increasing production costs there may also be loss of crop from the passage of the sprayer. Desiccation will not advance seed maturity and has a slow effect on green stems. However if the crop is infested with green weedy material or has a few late set pods which are still green, application of a desiccant will aid combining.

Application before the correct stage of maturity may result in reduced yield or loss of seed quality. The most widely used material is diquat. A non-ionic surfactant can be added. Apply when 90% of the pods are dry and black and most of the seed is dry. At this stage most of the leaves have senesced and fallen but the stems are still green. The contact action is fast and harvesting can be carried out 4-7 days later. It can be used on crops for animal feed, human consumption or seed.

Glyphosate can be used as a pre-harvest treatment to control perennial weeds. It must not be used on crops destined for seed.

Black bean aphid pressure is still high in bean crops although many field beans will be past the stage where yield impact is likely. Where pods are still filling in field beans or broad beans, aphicides should be applied when 10% plants are infested.

Sclerotinia in vining peas and green beans
Sclerotinia infection in vining peas has been relatively high in 2015 and the risk will remain high in areas where warm, humid conditions are being experienced. Late crops of vining peas and dwarf French beans continue to be susceptible to infection. Sclerotinia sclerotiorum affects a wide range of crops including vegetables, potatoes, linseed, oilseed rape and sunflowers as well as spring beans and peas (winter beans are affected by Sclerotinia trifoliorum).

Individual or groups of plants may be infected in discrete areas in the field. This is usually noticed in early to mid-summer when weather has been wet and warm. Stems become covered in white mycelium and may collapse as the infection develops. Infected stems and pods may contain black resting bodies, sclerotia, which are returned to the soil where they can remain for several years. As well as crop yield loss, pea and bean produce may be contaminated with sclerotia which are difficult to remove in factory processes.

Sclerotia in the soil produce small apothecia which release spores into the air. These adhere to stems or flower petals and infection invades the plant tissue. A rotation of 4 or 5 years without a host crop will help to reduce disease risk and, where the disease is expected, a preventative fungicide should be applied during flowering. Trials have shown that Switch, and Amistar at full rate, give good control of sclerotinia in vining peas and dwarf french beans.