Corn after Canola

How detrimental is sowing corn after canola?

Sowing corn after canola can result in corn being impacted by phosphorus deficiency, or what is commonly called “corn after canola syndrome”.  Phosphorus enters the corn plant through root hairs, root tips, and the outermost layers of root cells.  Beneficial fungi, called mycorrhizae, enhance P uptake in corn early in the season because the mycorrhizae strands increase the effective rooting volume of plants.  This is extremely important for uptake of immobile nutrients, such as P. 

In corn, up to 80% of early season P uptake is by mycorrhizae since the strand network may extend 8-12 inches from root.  Crucifer plants, such as canola, sugarbeets, and mustard, are not hosts for mycorrhizae so the mycorrhizae must regrow from spores.  This is why early in the growing season you’ll see corn suffering from P deficiency. 

Although the mycorrhizae eventually regrow and colonize the roots, the damage done by lack of P early in the growing season will have already occurred.  Yield may be impacted by the early season P deficiency, maturity of the crop may be delayed and grain moisture content at harvest may be higher (leading to higher drying costs).

The initial phosphorus uptake can be an issue but is this practice manageable?

To avoid ‘corn after canola syndrome’, producers should grow a crop less dependent on mycorrhizae for P uptake after canola (corn & flax are two of the most dependent crops). 

If rotation requires corn after canola, a “Plan B” is to supply high starter P levels to try and overcome any P deficiency problems that might occur. 

Variable results are seen with in-crop treatments to remedy phosphorous deficiency.   If products are tried, it is recommended to leave a check strip to determine effectiveness on crop recovery and yield. 


Have a follow-up question?

My soybeans are just entering the R6 stage, when could I expect to harvest them?

Typically maturity is reached when the plants hit the R8 stage of growth where 95 % of the pods are brown (i.e.mature color). The beans will need 5 to 10 days of drying after that before the beans are ready to harvest. From R6 –R8, you could be looking at 20-25 days depending on weather conditions.

Have a follow-up question?

Spraying for spider mites in soybeans

I found spider mites in part of one of my soybean fields. They haven’t done a lot of damage yet, and the soybeans are at R5 – R5.5. I’ve also heard that cooler temperatures, rain, and heavy dews slow them down. I will keep watching to see if they spread, but is there a point where it is too late to spray?

Spider mite populations are often higher when conditions have been hot and dry for a sustained period of time, but populations can change substantially after heavy rains. So if you are noticing what appears to be feeding from spider mites on soybean plants, and your area has had some recent rain, make sure to look for the mites and see what the current population is like. Spider mites are small (about 0.4 mm),  so tapping the leaves over something that the mites can easily be seen on may help in determining their presence and levels.

The stages of soybeans that are most susceptible to spider mites are the R4 (full pod) through R5 (beginning seed – when seeds are filling) stages. Once the soybeans reach R6 (full seed or green bean stage) the feeding from spider mites will have less impact on yield.

Have a follow-up question?