Rhubarb, garlic mustard and to-do list

By John Fulton

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[April 17, 2014]  Rhubarb and other fruits  A little bit of warm weather spurred some growth in many of our perennials. Then a hard freeze comes along and some of our plants may need some special care.

Of course, we can expect some fruit reduction in cases where severe frost or freezing catches trees in the stages of tender bloom and early fruit set. Book figures are about a 10 percent reduction in apples at full bloom with a temperature of 28 degrees. Peaches and apricots in early fruit set at similar temperatures will see about a 25 percent fruit reduction. An additional decrease in temperature to about 26 degrees magnifies the losses. Of course this isn't always bad. Many have been complaining the past couple of years about too much fruit and broken branches.

Of bigger concern is rhubarb. A hard freeze can actually damage leaf cells enough to release a toxin back into the leaf stalks. The leaves are always toxic on rhubarb, and if damaged enough to wilt or have black or brown along the edges, the toxin is almost certainly released. The solution is rather simple, at least this early in the game. Pull the stalks with the damaged leaves, and you get to start over with the regrowth. It may happen again as the plants have more growth, but at least now we are early enough we don't feel quite so bad about starting at ground level again.

For those who got some potatoes set out, if foliage is damaged enough to wilt, it is probably best to cut tops back to ground level and allow regrowth. Rotting back into the tubers causes more problems later on.

Garlic mustard

Garlic mustard is a cool-season biennial herb with stalked, triangular to heart-shaped, coarsely toothed leaves that give off an odor of garlic when crushed. First-year plants appear as a rosette of green leaves close to the ground. Rosettes remain green through the winter and develop into mature flowering plants the following spring. Flowering plants of garlic mustard reach from 2 to 3 1/2 feet in height and produce buttonlike clusters of small white flowers, each with four petals in the shape of a cross. We haven't reached the temperature threshold for the flower stalks to elongate, but that will come shortly.

Control of garlic mustard is somewhat difficult. Seeds can remain viable for at least five years in the soil. Small amounts can be pulled up (including the roots). Garlic mustard can regrow from root material.

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For herbicides, glyphosate (Roundup) is the most often recommended. Remember, glyphosate kills broadleaves and grasses when it gets on them. There has been some success with 2,4-D LV400 where there aren't concerns with other understory plants.

Very large patches have been controlled with fire, but that completely destroys the understory of timbers.

Remember to monitor garlic mustard areas for at least five years due to the seed dormancy period. Some action at this early time may help prevent larger problems down the road. It is much easier to control small patches than large ones.

The to-do list

  • Get ready to mow! Many are actually looking forward to the mowing duties after the winter we've experienced. Use a mower with sharp blades, and remove no more than one-third of the leaf blade  for a 2-inch mowing height, mow when grass is 3 inches tall.

  • Roses should have their final pruning any time now. It appears winter damage was severe on the Knock Out roses I've looked at. Cut back to green wood  hopefully you have some left!

  • Plant early garden now, if you haven't already. This would include things such as lettuce, spinach, onions from sets and other items that tolerate frosts. Hold off on those warm-loving plants such as tomatoes until after May 10.

[By JOHN FULTON, University of Illinois Extension director for Logan, Menard and Sangamon counties]

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