Root Crop Problems
Fortunately, root crops aren't bothered too much by insects or diseases, and the few that may strike can be prevented with a few good gardening habits.
Rotate your root crops as well as all other vegetables in your garden from season to season and in your early and late plantings. This discourages insects and disease.
Pest Control Basics
Make a daily visit to your garden, and pick off any harmful insects you see. Pull up and destroy any unhealthy or diseased plants. Or tear off the leaf or two that are infested and burn them. The rest of the plant may be fine.
Keep your soil healthy and productive by working in plenty of organic matter. Healthy soil means healthy and disease-resistant plants.
As soon as a crop is harvested, either till all the residues back into the soil or carry them off to the compost heap. By doing this, you don't furnish insects with a place to reproduce and live over the winter.
If, despite all your efforts, you do run into a problem with your root crops (root maggots, leaf miners, carrot rust flies or diseased roots, to name a few), get help from your local cooperative extension service agent or a master gardener. Knowing the area, he or she will be able to diagnose the situation and give you specific advice about treatment.
Your soil test alone may indicate a nutrient deficiency that might cause disease, and the extension service can be helpful in this case, too. For instance, sometimes a lack of boron in the soil will cause a problem known as internal black spot in beets. Your extension agent can give you the right prescription for adding boron to the soil (in the form of borax, a household product) to combat this.
If you're plagued by root maggots, wireworms or cutworms, a light application of wood ashes worked into the soil will help to deter them.
All in all, you shouldn't have much trouble keeping your root crops trouble free, if you practice the basic steps outlined here.
Rodents and Other Root Crop Lovers
Mice, rabbits and other small animals like nothing better than fresh carrots or beets -- both tops and bottoms -- for a midnight snack. You can protect your entire garden with a fence, but just keeping the whole area around the garden mowed and weed free also helps. If you use mulch anywhere in your garden, try to have it free of weed seeds, or you may be attracting seed-loving rodents to the garden without knowing it.