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Crop Crack 04.06.11
By Wendy Fearon
After a very cool wet May many farmers will welcome the drier warmer conditions to catch up on fieldwork. Crops are growing very rapidly at present and disease is now beginning to show. Last week we were concerned with crops not growing particularly well and this week attention is turned to growth regulator as fertiliser has kicked in and crops have become very strong.
Winter barley crops range from start of flowering (GS61) to end of flowering (GS69). Rhyncho & Mildew are present but levels are low where disease control has been maintained. Ramularia will now also become a threat to the upper plant, and underlines the need to control this disease in spring barley also.
Winter wheat crops range from flag leaf sheath elongating (GS41) up to ears 50% emerged, (GS55). Disease levels vary depending on fungicide programs & timings to date, with crops ranging from very clean to those showing high levels of both Septoria & Mildew.
The most advanced spring barley crops have the awns emerging (GS51-52) with most just approaching GS49. Straw stiffening may already be missed in the most advanced crops and should be done now in those fields thought to be at risk of lodging with recent growthy conditions.Cerone is the only product choice at this time. Westminster is still fairly clean with low levels of Rhyncho with Wagon & Quench showing a bit more disease.
Spring wheat’s have low levels of Septoria but Mildew is present on more susceptible varieties.
Potatoes
The very unseasonal gale force winds last week have broken many stems and leaves. Many of those leaves still attached have been abraded and bruised and parts of leaves are likely to turn black and die back as a result.
Crops are now growing rapidly as temperatures improve and consideration has turned to blight control where product choice and timing are extremely important.
There has already been blight reported in Northern Ireland. Products that have zoospore activity are the most effective 1st spray, applied at the rosette stage prior to rapid haulm growth.
RANMAN, SHIRLAN or TIZCA will control any zoospores that may be in the soil (either from ground-keepers or infected seed) and provide good protection of the new plant.
There are three different ways by which the blight fungicide moves through the plant:
Contact fungicides eg. DITHANE, RANMAN, SHIRLAN, TIZCA - these products protect only the outer surface of the leaf onto which they are deposited. They do not move into the leaf and therefore do not normally protect any new growth that emerges after application.
Translaminar fungicides eg. CURZATE M WG, HARPOON, INVADER, RESPLEND, REVUS - these products move into the leaf onto which they are sprayed and then redistribute throughout the leaf tissue as it increases in size. They become rain-fast once they are in the leaf.
Systemic fungicides eg. CONSENTO, FUBOL GOLD, INFINITO - these products move in through the leaf surface and upwards into the new growth that emerges between applications, protecting that new growth from infection also.
Because of the considerable amount of new growth being produced during the rapid canopy development phase it is essential the product being used is fully systemic to properly protect the new leaves being put on between applications. Later planted crops are higher risk as they produce more new growth between applications than earlier planted crops, at a time when the level of inoculum in the air is progressively increasing.
Of the fully systemic fungicides, only those based on propamocarb appear to effectively control the A2-13 genotype. CONSENTO is a new systemic product from Bayer, containing propamocarb and fenamidone. The fenamidone adds a different mode of activity and builds in early tuber blight activity also. (Bayer have discontinued MERLIN & TATTOO and therefore are no longer available.) CONSENTO controls all strains of blight, with no resistant genotypes found to date. Although in terms of mode of activity they are translaminar only, RESPLEND and REVUS also give very good protection of new growth and are very effective alternatives to propamocarb.
Grassland
Grassland herbicides use growth function to kill weeds, therefore peak growth periods should be used for herbicide application. There must be sufficient growth to allow herbicides to be effective and vegetive growth is the key time to apply, as the chemical then gets drawn down into the roots.
Herbicides are less successful once plants have progressed to the reproductive stage and have thrown a stem or began to seed. Once weeds are beyond the ideal growth stage for spraying they should be mown or topped and allowed to regrow again, and a herbicide applied to the fresh young growth.
To optimise efficacy of any herbicide, recommended water volumes should be observed, even when it means more time spent spraying. It is important to note ragwort plants in their second year are now coming close to flower and should be sprayed immediately as flowering ragwort is poorly controlled. The routine herbicide treatments for this weed are full rate MCPA or 2, 4-D, and they are most active on growing rosettes with reduced activity as the stem starts to extend. They are not clover safe. You can use a mixture of both these products as Nufarm Lupo which allows an increased dose herbicide compared with either alone, with a consequent activity benefit. Stock must be kept of until the weeds have rotted away, which can take up to six weeks.
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