PGRO Crop Bulletin

Number 6. 24th May 2010

Post emergence herbicides Generally pea crops are now at a stage where a post-emergence herbicide application may have to be considered because dry weather in many areas has meant poor pre- emergence weed control. Options are limited to bentazone products such as Basagran and Troy 480, MCPB (e.g. Bellmac Straight, Butoxone, Tropotox) and MCPB + MCPA (Impetus).

Most of the varieties shown on product labels are no longer grown and when considering varietal tolerance it is advised that ‘PGRO should be consulted regarding any variety not mentioned’. Other than specific product restrictions e.g. bentazone use in forage peas, all combining pea varieties on the PGRO Recommended List and the newer vining pea varieties on the PGRO Descriptive List are tolerant of the above applications as long as label instructions are followed e.g. enough wax is present, the crop is not under undue stress (drought), if temperatures are in excess of 21°C etc.

Higher temperatures mean better weed control but potentially more crop effects and with the hormones this means increased epinasty but the crop should recover. If daytime temperatures are above 21°C then applications in the evening should be considered to minimise the potential for crop damage.

PGRO work on crop safety is based on full rate and double rate applications so using reduced rates should lessen the chances of crop damage further.

Disease control in winter beans Winter beans are at about five or six flowering trusses and some crops may just be starting to show first pods enclosed within the flower on the bottom nodes. There is still very little disease present but where chocolate spot is visible on the lower leaves sprays should be applied.

Disease in spring beans There are signs of downy mildew infection in some spring bean crops and, again, these crops should be monitored. Look for a greyish-brown, felty growth on the under-surface of leaves. Some varieties have good tolerance to the disease. Spray at early flowering where the disease is present on 25% of plants. For further information about the disease and the risk in your area go to www.cropmonitor.co.uk

Pea moth A few pea moths have been caught in traps. Where thresholds have been reached, crops will not be ready for spraying until they have reached first pod. Spray dates are available through the PGRO telephone service on 01780 783099. See PGRO Technical Update 149 for details. Traps are available from Oecos tel: 01438 832481 Tortrix moth There have been a few reports of tortrix moth in peas and spring beans. As flowering approaches the upper leaves of the plant are tied together with a fine, white web and have a bunched or hooded appearance. Within these webs the caterpillar can be found feeding on the plant. Caterpillars are dark greenish-brown, pale underneath and with a shiny golden head. They should not be confused with Silver-Y moth caterpillars which are bright green with a dark stripe along the back. Tortrix caterpillars do not cause significant damage and no action is necessary.

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