3 May 2011

Gerrmination of sclerotia still increasing in the south west and apothecia are present in the north and west where soils are moist. Petal tests indicate that sclerotinia spores are present in all regions including the east despite continuing dry weather. High risk conditions expected when it rains especially in the west and north. Continue to protect crops with sclerotinia fungicide treatments whilst crops are flowering.

Weather conditions and oilseed rape growth stages

Overview: Flowering has progressed rapidly in the last week and large numbers of petals have fallen in dry, windy weather. Most crops are at the mid- to late flowering stage (GS 4,5-4,9, BBCH 65-71) with some still at early flowering stage (GS 4,1 BBCH 61). Pod formation is underway with more than half the pods well formed in many crops. Forward crops have almost finished flowering.

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There has been 4% new germination in the Devon this week to give a cumulative total of 21%, but no change at the other depots. There is still no germination at sites in the east as soils remain very dry and cracked. However, germination could be underway in any region where there has been heavy rain. A scattering of infection periods are being forecast at the moment. Night temperatures are now sometimes above the 7ºC minimum temperature required for ascospores to germinate and infect the plant. Petal tests are showing sclerotinia is present in all crops tested so far and at high levels in the west in fields with a history of sclerotinia. Petal infection is also present in the east where depot germination is restricted by dry weather and protectant sprays are still advised. If recent rain resulted in petal sticking, some sclerotinia infection could be underway.

Some petal sticking has been noted in Devon. The current disease risk has changed to high in the south west, west and north as crops approach the late flowering stage. In the east, dry conditions are restricting sclerotinia activity but there is still a risk where sclerotinia occurs regularly.

Many crops have now had one fungicide treatment for sclerotinia. For a twospray approach, the first spray is usually at early flowering with a second spray about 3 weeks later. Sprays should be timed to ensure crops are protected during flowering.

High levels of light leaf spot are present in some crops in all regions and many crops are at risk in the north. Control of light leaf spot should now be part of the decision making process for selecting products for PGR and sclerotinia control.

ô€‚ƒ SE and East Anglia – Flowering is likely to be completed on the main raceme during the next week in forward crops but could continue on secondary branches. Most areas have hardly any rain recently, but where there was localised rainfall in the last week, this could increase risks up to the end of flowering. More rain is required to produce active germination though, judging from the first petal tests at Boxworth, crops in fields with a history of sclerotinia could be at high risk if petal stick occurs.

ô€‚ƒ SW and West –Many crops are at mid- to late flowering; a few are still at early flowering. There has been more sclerotial germination at the Exeter depot but not at the Hereford depot this week. Cumulative sclerotial germination remains highest in the Devon depot at 21%. A little new petal sticking has been reported in the south-west. The regional risk is higher than in other regions and high levels of sclerotinia have been found on petals in some fields. With further unsettled weather in prospect it is important to protect plants against infection whilst they are flowering.

ô€‚ƒ Lincs, and E Midlands – Most crops are in full flower, but a few are struggling with considerable loss of flower buds. Soils have been dry at the surface and yet more rain may be required to stimulate sclerotial germination. Low numbers of sclerotia may be germinating in crops in the region, as petal tests at Boxworth and Terrington indicate air-borne sclerotinia spores are present in crops despite the dry conditions. Sclerotinia activity and hence risk could increase where there has been heavy rain.

􀂃 N England - Many crops are at mid- to late flowering strongly and late crops are at the early flowering stage. There has been no new germination in the depot near Malton since last week and the total is still 5%. The north appears to be at risk this season, probably more so than the east at present. Where there has been heavy rain in the last week there could be high risk conditions. Be prepared to maintain protection of crops if more rain is expected. Light leaf spot is more active than last season and has become more obvious on the younger leaves.

Key points

Germination has continued slowly in the south-west this week, but fruiting bodies are still evident in the west and north. It is still too dry in the east. However, petal tests are showing sclerotinia spores are still being produced. There is likely to be higher risk where showers provide conditions for petal sticking.

Petal infection results

The % petals infected with Sclerotinia spores will be determined at the 6 monitoring sites at 3 different times during flowering - first flower, early flower and mid-flower. This supplements the sclerotial germination records and shows the degree of spore production and survival.

The initial results from the first tests indicate there may be high levels of petal infection at high risk sites in the west. In the east, there is some petal infection even though dry weather appears to be restricting germination.