CROP CRACK - 30.06.07
By WENDY FEARON
Clarendon Agricare - Grassland Management

The mixed weather conditions this season has left farmers considering weed control options for second and third cut silage. Weed control after cutting is crucial to maximizing both yield and crop quality. Problem weeds such as docks, nettle and thistle should be sprayed in their regrowth period.

GRASSLAND

Grassland herbicides use growth function to kill weeds, therefore peak growth periods particularly at this time of year 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 optimize efficacy of any herbicide, recommended water volumes should be observed, even when it means more time spent spraying. For a broad spectrum herbicide such as Forefront this should be 200 litres/ha and Doxstar, 300 litres/ha minimum.

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.

POTATOES

Blight is now very active in all parts of the province. It is therefore essential to inspect crops frequently for signs of the disease and to keep spray intervals as short as possible, appropriate of high to extreme risk conditions.

In late planted crops that are still putting on new growth spray with a systemic such as Tatoo.When the period of rapid growth is over it is advisable to change from systemic to translaminar products such as Infinito,Curzate M or Invader. Aphids are present on some crops and it is important to monitor numbers.

WINTER CEREALS

Winter barley crops are now well into the ripening stages and with better weather cutting will begin around the third week of July. Some of the early drilled wheat’s will not be far behind. Most early sown winter wheat crops are now past the flowering stage, with more advanced crops at the early milk development stage (G.S. 73-77).

Septoria tritici is present to a greater extent in most crops with some mildew also present.  There are also some reports of yellow rust and this disease needs to be treated quickly to prevent rapid spread.

Ear wash fungicides (T3) are important to keep grain quality high.  With at least 4 weeks to go before ripening begins, it is essential to apply a good head spray to keep the head free from disease and maximise grain fill. A good T3 treatment will control late developing Septoria Nodorum (glume blotch), as well as Tritici, a range of late season ear moulds and Fusarium that produce mycotoxins on the grain if not controlled. Dirty, darkened ears with a shriveled pickle are a common site in August, where a good head spray has not been applied. All of these ear diseases are favoured by damp and humid weather especially at the grain ripening time.

The T3 spray should ideally be applied sometime around the 4th week after T2, up to the latest timing for the product. The physiological effects of strobs have clearly proved their value at this time in maintaining green leaf area and boosting grain-fill, and therefore should also be included in this final treatment. A mix such as Prosaro and Twist are very effective and can be applied up to milky ripe (G.S.83) as can Folicur.

Check the ear regularly for aphids. If found in large numbers spray with Decis Hallmark or Sumi-Alpha to prevent damage.

SPRING CEREALS

Most spring barley crops now have the head fully emerged. Mildew levels have decreased whereas rhyncho and septoria levels have rapidly increased. Both barley and wheat crops would benefit from a fungicide treatment.Mantra, Midas or Mobius should be used on barley and spring wheat should be treated with either Prosaro or Mantra.

PRE-HARVEST WEED CONTROL

Winter barley, early sown winter wheat and spring barley crops should be examined to decide whether or not they require pre-harvest treatment for the control of annual and perennial weeds especially scutch, rough stalked meadow grass, thistles etc.There are many different formulations available. Independent trials carried out over the last couple of years in GB looking at the effect of using Roundup Gold in various replicated treatments consistently showed moisture contents were reduced by 2.0-2.5% at harvest compared to plots where no treatment was applied. The biggest shifts were recorded where strobilurins had been used. Roundup Gold and Roundup Biactive should be applied once the grain moisture gets down to 30%or below, ideally 10-14 days (and not less than 7 days) before cutting.

HORTICULTURE