OSR - Yield Constraints
Agronomists from large Agrochemical distributors often pose the idea that drilling conventional oilseed rape (OSR) at the beginning of August is a good idea.
Autumn 2020 has provided sufficient early soil moisture to make early drilled crops look a success at this early establishment phase.
Of course where flea beetle is a likely problem early drilling gets you past issue – doesn’t it? Some reputable entomologists have gone into print stating this is not “exactly correct.”
However drilling OSR to early has its draw backs.
1) You need an early-to-harvest crops, such as winter barley.
2) If you drill OSR early, you’ll have more problems with light leaf spot because the crop is exposed to ascospores for a longer period of time.
3) Depending on your rotation you are likely to increase the occurrence of clubroot. Trials from 2016 resulted in an 80% reduction in clubroot just by drilling “later.”
4) Although Alternaria and powdery mildew are less common, sowing early is likely to increase their prevalence.
5) There is some evidence that earlier sowing favours Verticillium wilt infection.
6) Earlier drilling also increases time the crop is exposed to phoma infection this allows the disease to complete its life cycle and cause more damage to the crop.
7) Cabbage root fly is likely to occur more commonly with young seedlings being killed off.
8) Aphid is more likely to be found within the crop increasing the risk of virus infection.
9) Turnip Sawfly can become a problem the caterpillar feeding damage causing plant loss in affected crops.
10) Grass weed control can be more challenging, whether it is blackgrass or brome.
11) Broad leaf weed numbers increase and become larger in size. Some we have no complete control for and so they decrease yield and affect harvest quality of the OSR seed.
If each item takes 1% off your final yield that is an 11% penalty from “early drilling.”
A quick “Fag Packet” financial calculation provides us with:-
A crop averaging 4.5 t/ha now averages 4.0 t/ha (minus 11%)
Very conservatively if each operation cost £5.00/ha to correct that’s £55.00 to come off the bottom line
Selling at £320/t
Total value £320 * 4 = £1280.00
Return = 1280 – 55 = £1225.00
Growing a crop yielding 3.8 t/ha will provide a similar return without the need for “additional cost” or additional risk or additional work load.
1225.00 / 320 = 3.83
At least it’s established and in row!
Seedling thistles and Hedge mustard.
A few black grass plants and the odd cleaver
Cabbage leaf miner (Phytomyza rufipes) often causes noticeable mines in the lower leaves of autumn-sown rape. As oilseed rape plants can tolerate loss of older leaves, treatment with insecticides is not normally considered to be necessary.