Reseeding and dry conditions

May 24, 2018 – Issue 8

Wind losses, intense flea beetle feeding and slow emergence – each made worse by dry conditions – have some farmers wondering about reseeding. Keeping a thin stand is often the better option, but this article will help with the decision.

Let’s deal with the third reason first: If dry conditions have slowed emergence, stranding seed in dry soil, going in again to seed deeper probably isn’t the right solution. Going deep will further dry out the top soil, and when it does rain, you’ll have two batches of seed emerging. Each batch will likely emerge at distinctly different times.

As for wind losses due to sand-blasted seedlings or seed blown out of the ground, it can happen in small patches. Losses of large areas due to wind would be rare (but can happen). Heavy losses from flea beetles can occur too, and can be worse in dry conditions when seedlings have just enough moisture to emerge but not enough moisture to grow very fast.

When growers have canola stands dropping to 2 plants per square foot — for whatever reason — they grapple with the question whether to reseed. A canola stand with as few as 1-2 plants per square foot (evenly distributed) established in May usually has higher economic potential than a canola crop reseeded in June. (Neither will have the yield potential of an early crop with a good stand.) One to 2 plants is far below the minimum 5 per square foot required to meet yield potential, but a thin stand seeded early has greater economic potential (considering yield, quality and cost of production) than an adequate stand that doesn’t get established until mid to late June.

However, reseeding may be the better option if:

—The stand of 1-2 plants per square foot is not uniform. If large areas of the field have no plants while some areas have 5-10, for example, this field will not likely have the same yield potential as a field with 1-2 plants, or more, spread evenly across the field. A uniform plant stand is crucial at low plant populations.

—Weeds are large and outnumber the crop and cannot be controlled effectively with in-crop sprays.

—Crop insurance will pay a reseed benefit and/or seed companies have reseeding rebates on seed. This helps with the economics, especially in May when a reseeded crop still has time to reach its yield potential. Choice of seed is another factor. A 2010-12 study at Western Applied Research Corporation (WARC) in Scott, Saskatchewan, found that re-seeding to the same full-season variety in early June resulted in significantly higher yields at 50% of sites compared to the low plant population control (fewer than 4 plants per square foot) seeded in mid May. The study found that the chances of getting No. 1 grade are lower with canola reseeded in June in this situation, but higher yield potential and a crop insurance reseed benefit can make up for it about half the time.

The WARC study also found that: (1) Re-seeding in early June to a slightly shorter season variety (9350RR) resulted in higher yields than the earlier-seeded low population control at only 25% of site years. (2) Reseeding to Polish canola, as an alternative to a shorter-season napus, did not help. (3) Reseeding in mid June did not pay.

Final considerations in the reseed decision, as outlined in the study, are to look at the current and forecast moisture situation to make sure the reseeded crop can emerge quickly, and keep in mind that big plants from a thin stand may provide harvest challenges in terms of variability.

Questions for growers to answer:

What are the details of your crop insurance reseeding benefit?
Does your seed company offer a reseed benefit for canola?

Further considerations:

—Can growers give the crop a few more days? Waiting will give a better impression of how many seedlings survived and will give ungerminated seed a chance to emerge and contribute to the stand. If growers have crop still to seed, consider seeding those fields then come back to the reseeding question. Reseeding in late May will have nearly the same yield potential as reseeding in mid May.

—If growers do decide to reseed, consider leaving a few strips of the original stand as a test. Compare management issues for both sides through the year and yield results. This may help with future reseeding decisions.

—How to fertilize the reseeded crop. If soil has low baseline P levels, some seed-placed P may benefit the reseeded crop (and this provides another opportunity to boost P levels). If soil reserves are medium or better and soils are warm and moist for rapid early growth, extra P may not be required for the reseeded crop. Sulphur and nitrogen should not be required for the reseeded crop, provided these nutrients were applied at required amounts the first time.

—Spray out the first crop. If the stand is less than 1-2 plants per square foot, growers may still want to spray them out to eliminate the competition. These few more mature plants will not contribute to harvest yield, and the competition will take nutrients and moisture from the reseeded stand. Burnoff applied prior to the reseeded crop will also manage weed growth that may have occurred since the first burnoff. If growers are concerned about getting the reseeding done (or maybe there isn’t a good spraying day in short term), it may also make sense to seed a different HT system and spray out the previous crop in-crop.

—Reseeding is not just about yield potential. By reseeding, growers can avoid the season-long headaches that come with managing a thin stand.

Canola Watch