By David Jones, Broad Acre Agronomist

Fall Armyworm are definitely active in wheat crops now, and this week I have picked up some interesting observations and tips on what to look for.

And in canola crops, Meru County has been experiencing perfect conditions for one of the major diseases of Canola globally, so it was only a matter of time before it appeared in Kenya…

Phoma Stem Canker

Last week I saw the first Phoma lesions in Canola that I have seen in Kenya. Phoma can be a significant disease of canola that causes stem cankers to form and restricts nutrient and water movement up the stem.

The threshold that I apply before treatment with a fungicide is 10% of plants infected at 3-4 leaf stage. However, larger plants are more able to resist the disease, which takes longer for the fungal infection to travel down the leaf and into the stem.

Phoma Stem Canker disease in canola causes stem cankers to form and restricts nutrient and water movement up the stem.

Fungicides containing tebuconazole, prothioconazole and difenconazole are highly effective against the disease, which is worse in damp conditions around 15-20°C. From my experience no-till situations tend to create notably higher pressure as the disease spreads from spores on trash from previous canola crops.

Scout fields carefully in cool, damp conditions

One important point to realise when scouting fields is that the severity of lesions does not always correlate with varietal resistance; some resistant varieties still show lots of phoma lesions, but have a combination of genes which prevent or slow the formation of Stem Cankers. Scouting for Stem Cankers after harvest is really important, and also helps review Sclerotinia levels.

For many varieties there is simply not a lot of data produced, however our Canola variety trials will start to build our experience over the next few seasons and I feel that Timau will be a very important place for testing Phoma resistance!!!

Pick the right fungicide and look at independent data

There is good, independent data on fungicide performance thankfully, this time from the AHDB in the UK. Cirkon (propiconazole + prochloraz) and straight Tebuconazole give a modest reduction in Stem Cankers (photo below) but full label rates are required, so don’t skimp.

Cirkon (propiconazole + prochloraz) and straight Tebuconazole give a modest reduction in Stem Cankers

Be very aware that Tebuconazole has great growth regulatory properties above 200g/ha of active ingredient in Canola, so on slow crops being attacked by pests, be careful!

A far better product in Kenya is Prosaro which contains Prothioconazole and Tebuconazole (at a lower rate so less growth regulatory effect). Difenconazole is also a very useful product, but it won’t give incidental control of Sclerotinia like Prosaro. Note the yield effect from Prosaro in the right hand graph too, but remember to mix actives through the program so don’t become reliant on it.

Be on Alert for Fall Armyworm

In the last few weeks I have found incidences of Fall Armyworm in wheat crops as I reported in recent #ThinkAgronomy updates. One thing I have noticed is that the larvae can be very hard to find, and as a result the damage is confused or not recognised.

The threshold temperature for the survival of the larvae is 10.9°C, which is probably why we have seen damaged plants but not found the larvae, with the recent cooler nights.

Note that even when ears are fully emerged, Fall Armyworm appear to be more elusive than Bollworm and tend to feed lower in the canopy rather than on the ears, and always early in the day.

Fall Armyworm is on the left; a “hole punch” effect from where the larvae has eaten through the yet to emerge leaf while it is rolled up.
On the right is Cereal Leaf Beetle; they look dramatic but the damage is often not worth treating

With Fall Armyworm, look for:

 

About David

 

David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.