Canola - factors to consider from June - September

July 2015

Canola is a very important crop and there are a lot of management factors to be taken into account to make a success of canola.

There are some pests and diseases that are important and it must be controlled, because these diseases and pests have a big influence on the yield of canola.

Diseases

Blackleg (Leptosphaeria spp./Phoma lingam)
This disease is very important, because it has a big influence on yield. The right management practices must be applied to minimise the negative effect of this disease.

There are currently two fungicides registered on canola for the control of Blackleg. These fungicides must be sprayed between the 4 - 6 leaf stages of the plant.

Stem rot (Sclerotinia sclerotiorum)
This disease becomes more important because the hectares under canola are much more than a couple of years ago.

Sclerotinia has a very wide range of hosts and attacks lupines, soybean and sunflower among others. The symptoms appear during flowering or thereafter.

The following conditions must be present for a Sclerotinia outbreak. Wet conditions for at least 10 days at the soil surface in mid to late winter, with temperatures between 10°C - 15°C for the Sclerotinia to germinate and trigger spore release. Warm moist conditions with temperatures between 20°C - 25°C for stem lesion development.

The most characteristic symptoms of the disease occur at the bottom of the stems of plants. Light bleached spots with slightly grey middle portions can be seen on the stems, usually at the point of attachment of the leaves or lateral branches.

The fungus does not form spores on the affected plants, but a dense bundle of white hyphae, where the Sclerotinia can be seen in the stem. The Sclerotinia can survive for up to seven years in the soil. It is very important to practice crop rotation with non- host crops such as barley, wheat and oats to minimise the incidence of Sclerotinia stem rot.

Insects

Cabbage aphid (Brevicoryne brassicae)
The cabbage aphid is currently the primary species that feeds on canola. Canola is extremely sensitive to aphid infestation during the early growth stages. Heavy infestation during the flowering and pod forming stages may prevent flower formation and may seriously impair the setting and filling of pods. This has a big influence on yield. If moisture stress occurs it is important to protect canola from aphids. Threshold values: 20 % of plants are infected.

Diamond Back Moth (Plutella xylostella)
This is an insect that is generally underestimated and the damage that is done is more than we think.

Depending on the ambient temperature, the adult insect (the moth) is usually noticed during the stem elongation phase. The light green larva eats holes into the leaves. Pods are also attacked, but the damage is usually superficial and pods are seldom penetrated, however, damaged pods tend to shatter more easily. There is more than one generation per season.

Threshold values: Middle to late flowering: 17 to 23 larvae per 10 plants. Pod filling: 43 to 57 larvae per 10 plants.

Sampling is very important to detect this insect early and to control it. When the temperature is high the Diamond Back Moth tends to multiply very quickly. Consistent and regular inspections are very important to control these insects to minimise the effect on yield.

Article submitted by Jannie Bruwer, Bayer Crop Sciences Area Manager, Southern Cape.
For more information, send an email to jannie.bruwer@bayer.com.

Publication: July 2015

Section: Pula/Imvula