Plant Disease


Lately the calls to the UConn Home and Garden Education Center have been about preparing for winter. People want to prune trees while it is still warm. Pruning for most trees is best done while dormant, in winter cold. Trees really don’t need to be pruned at all, just let them grow into their natural shape and size. If you have a tree or shrub that has outgrown the spot where it is planted, than replace it with a more appropriately sized plant. I have seen many houses where the Rhododendron maximum has taken over entire picture windows! I can only wonder how the view from inside looking out appears. Those plants need to be ripped out and replaced with something that has a much smaller height once it reaches maturity.

Lawns are popular topics on the phone and email contacts. Folks, it is too late to fertilize your lawns now. The plants are going into dormancy. This means they are not actively growing. We know they are not growing because we are not having to mow the grass. If the plants are not growing, they are not moving very much water through their roots up to the leaves. Fertilizer is water-soluble, taken in by the plants once dissolved in the water. So if plants are not picking up the water, they are not picking up the fertilizer either. The fertilizer does not just sit there waiting for the plant to take it. The fertilizer will be washed away with rain and snow, moved down and out of the reach of grass-roots in the spring when the plants wake up and start moving water again. Wait to fertilize lawns until you have to mow again in the spring.

Vegetable gardens need to be cleaned up now. Cut back the asparagus and destroy the stalks by burning or bagging and place in the household trash. Asparagus beetles can overwinter on the dead foliage. Tomato and pepper plants need to be pulled and composted deep in the pile. Clean up all other plant material for a fresh start in the spring. Turning the soil over once will expose overwintering pests living in the soil to the colder temperatures and birds to eat. Try planting a cover crop for tilling in during the early spring. Have a soil test done to determine pH and nutrient levels. Lime can be applied in the fall to work all winter if needed. I plant spinach and cold tolerant lettuces in a bed under a hot cap. It is a frame of plumber’s pvc pipe made into a triangle and attached to 2 by 4’s then covered with painter’s plastic sheet stapled to the wood. We attached hinges to one side of the 2 x 4’s and to the side of the raised bed. Once the seeds germinate, their roots will grow as long as the temperatures are not below freezing. The small plants just hang out all December and January, waiting for the about the last week in February when the days get longer, to start growing into strong, large plants. Picking baby leaves begins in the middle of March. I love picking my own fresh salad while standing in a dusting of snow!

Other end of season garden chores include digging the tender bulbs, tubers and corms for storage in non-freezing temperature. Dig gladioli, dahlia tubers, canna and caladiums. They can be stored in damp peat moss, saw dust or sand. I keep mine in a wooden box in the hatchway  of my home. This area stays between 40 and 5o degrees F, perfect for these plants. I am even trying to save my ornamental sweet potato vine tubers. I will let you know how that turns out! As for herbaceous perennials, I cut them back to the ground to prepare for winter. This eliminates any disease from next year’s growth and hopefully removes overwintering insects, too. Cleaning up the foliage of this year exposes hiding places and homes of mice, chipmunks, moles and voles. Anything to rid my garden of these critters, I will try. Set old-fashioned snap mouse traps near any holes in the ground you find. I have caught mice, voles and chipmunks all in the same small area.

Happy End of the Garden Year,

-Carol

This summer we had an interesting tomato disease in the diagnostic lab.  It’s tomato pith necrosis, caused by the soil-borne bacterium Pseudomonas corrugata

Necrosis and wilt symptoms on tomato plant caused by tomato pith necrosis.

The earliest symptom is chlorosis or yellowing of the younger leaves.  As the disease progresses, leaves may wilt and become necrotic (dead).  Infected stems may or may not have visible dark lesions.  The sample received in the lab this summer didn’t have this symptom.  The primary symptom in this case was wilting and necrosis of the upper part of the plant. 

To investigate further and to check for wilt diseases of tomato, the lower stem was cut in half longitudinally.  The characteristic symptom of tomato pith necrosis, a chambered or hollow pith or center of the stem, was observed.  In some cases, this is white as shown in the photo.

White chambered pith in tomato stem.

More advanced bacterial colonization results in the browning and softening of this tissue.  The vascular system may also be brown.  This tissue is in the outer part of the stem and the sample’s vascular browning is pictured below.  Two wilt diseases of tomato caused by fungi, Fusarium wilt and Verticillium wilt, both cause browning in the outer, vascular tissue of the stem, but not in the pith. 

Stem section with both vascular and pith browning.

White and brown (decayed) chambered pith.

One symptom that is quite distinctive but that was not readily apparent in this case is the development of many adventitious roots on the outside of the stem near the chambered pith areas.  Adventitious roots are roots that develop from above-ground plant parts.  Sometimes, the infected tomato plant is able to grow out of this disease. 

 Conditions that favor tomato pith necrosis include low night temperatures, high nitrogen fertility and high humidity.  It often occurs when the fruits are nearing mature green, or just before they begin to redden. 

To prevent this disease, do not over-fertilize with nitrogen and space, prune and stake tomato plants to promote good airflow around them, reducing humidity. 

JA

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