Repairing drought-damaged swards

Last year was a tough year on grass. From a plant agronomy point of view, the drought was a lot harder on grass than the cold spring. The cold prevented grass from growing normally, but it didn’t really damage it.

The drought, on the other hand, did do lasting damage to some grass swards.

The amount of damage done was variable, both between farms, fields and even within fields.

Tiller death mainly occurred in patches. I’m not sure if this was because that particular patch had a higher cover than surrounding patches, or if that patch had grass of all the one variety which was less resilient to dry conditions or if it was because of excessive nitrogen loading in a urine patch.

A low post-grazing height during the drought could be another cause of plant death, especially if the sward was grazed below the growing point.

Either way, there are sections and patches in fields that are now occupied by chickweed where there was once perennial ryegrass.

In some cases, the chickweed is taking up a couple of square metres but in other cases there is just bare ground in between perennial ryegrass plants that survived.

What to do

What to do with these areas now depends on how severe the problem is. Chickweed is an annual weed, meaning it won’t last past one season. However, it will shade out grass and spread further if not controlled. If the cows graze the chickweed it won’t grow back.

Grazing is a good control method but this won’t always be feasible or the cattle won’t always graze it.

Chickweed is relatively easily controlled by herbicides.

However, grass should be growing well before spraying or else grass growth could get checked. The other thing to watch when selecting a herbicide is that it should be clover-safe if there is clover in the field.

Also, watch the time period between spraying and grazing again.

Some herbicides require 10 to 14 days between spraying and grazing. This is a tight enough window if planning to spray in April when grass is usually growing well.

Bare patches

When the chickweed is controlled, the next decision is what to do with the bare patches. Large areas of bare patches (more than one square metre) are problematic and will need to be sown with grass seed.

If the remaining grass is of good quality, that is a high percentage of perennial ryegrass, the field could be over-sown with grass seeds.

Graze tight and over-sow using a tine harrow/grass seeder combination. Sow at half rate and roll after sowing. Graze tight for the next few rotations and avoid cutting that field for silage.

If the remaining grass is of poor quality, then a full reseed might be more pragmatic.

This will involve spraying off the existing sward. In this case, you wouldn’t spray the chickweed first as the glyphosate spray would kill that anyway. Reseed the field as normal. See here for details.

Success

In some cases, regular tight grazing will solve the problem without using any sprays or any over sowing. For this method to be successful, the sward must have a high perennial ryegrass content and the soil fertility should be good.

If soil fertility is poor or if not enough nitrogen is available to the plant, its ability to tiller will be lessened.

The recovering sward should be grazed to a post-grazing height of 3.5cm to 4cm for every rotation. Pre-grazing covers shouldn’t go above 1,400kg and no silage cuts should be taken from the field.