Occasional spots of rust can be seen in some crops and the first cases ofpowdery mildew are now becoming apparent in Suffolk. Hot dry weather willencourage the development of powdery mildew while warm, damp conditions willfavour the development of rust. Either way, now is the time to check yourcrops for disease with your area manager or agronomist and, when found, toapply a full rate broad-spectrum fungicide to control these foliardiseases. All crops will require at least one spray, with those scheduledto be harvested from October onwards likely to benefit from a second spraylater on. We will keep you updated of disease pressure as the seasonprogresses.
Some crops have lost their bright green appearance and such paling oryellowing of leaves can be caused by nitrogen deficiency. Often this istransient following periods of exceptionally heavy rain as we have seen inplaces this year.
As well as chlorosis, nitrogen deficiency can reduce leafinitiation. However, previous work has shown that an increase in sugarconcentration during the early stages of deficiency compensates for thereduction in root weight thereby not affecting total sugar yield. Otherwork has shown that while topping up the nitrogen supply does cause an increasein the growth of root and tops, sugar is accumulated less rapidly than inplants that were maintained on a low N fertiliser. The outtake from this workis that the effects of nitrogen deficiency cannot be completely reversedthrough the application of additional nitrogen.
There is no new evidence of any benefit of applying moreN, and so there is no justification for applying more N to any crops at thistime. However, as part of our ongoing studies we have initiated a newpiece of work to look at this again with current varieties, grown under modernfungicide regimes. We will report on the findings of this trial in duecourse.
A number of other factors are also causing yellowingsymptoms in some crops such as virus yellows, or indirect consequences of downymildew infection or nematode attack. Also, this week, the first case ofrhizomania for 2014 has been reported. It is in the Orford area and allindications are that it is of the AYPR strain (further testing to becompleted). The warm spring and heavy rain events have combined to createconditions which have been favourable for the development of rhizomania.
Black grass is currently flowering and will soon form viable seeds. Forfuture reference it is a good idea to make maps of weed patches, especially inthe case of black-grass. If you suspect resistance but do not know thestatus of your black grass think about resistance testing. Severalcompanies offer the service and you should check before collecting seed what isrequired. Generally speaking, seeds should be collected once they aremature and starting to shed. They are best collected on dry days and asmall cupful is required. If not fully dry, air-dry the seeds in an opentray before sending for testing.
Weed beet and bolters
Weed beet and bolter control is continuing. Seed return from uncontrolledweed beet and bolters is massive and will lead to a rapidly increasing problem Remember, also, that weed beet at densities of only 1 plant/m2 can reducedsugar beet root yields by 11% making their control crucial if this years yieldpotential is to be maximised.
Key points are:
- Do not weed wipe once roots are of a harvestable size this can potentially lead to rotten roots entering clamps or the factory
- Where cutting is being practiced continue with secondand third cuts at three week intervals
- Where weed beet is a problem, look at the croppingrotation and extend the interval between beet crops where possible
- Plan forward to control weed beet in all crops in therotation
A list of Weed Beet and Bolting Contractors can befound at www.uksugarbeet.co.uk