Turnips, members of the Brassica family, are valued by home gardeners for their dual harvest of leafy greens and swollen root vegetables. They are a cool-season crop that offers a quick yield, but their health and quality can be easily compromised by various biological and environmental threats. Understanding these common problems and implementing timely solutions is the most effective way to ensure a successful harvest. This guide provides practical steps for identifying and managing the issues that frequently affect turnip growth.
Identifying and Controlling Common Turnip Pests
Flea beetles are a frequent and damaging pest, particularly targeting young turnip seedlings. These tiny, dark-colored beetles jump rapidly when disturbed and leave behind a characteristic “shot-hole” pattern on the leaves. Severe feeding can stunt a young plant’s growth or even cause it to die. Reactive control involves applying insecticidal soap or neem oil directly to the foliage.
Aphids are soft-bodied insects that congregate on the undersides of leaves and growing tips, sucking the sap from the plant. Their feeding causes leaves to curl, become discolored, and often leaves a sticky residue called honeydew, which can lead to sooty mold. For localized infestations, a strong stream of water can dislodge the aphids, or use insecticidal soap or neem oil to treat affected areas.
Root maggots pose a threat below the soil line, primarily affecting the developing turnip root. These white or yellowish larvae, the offspring of a small fly, tunnel through the roots, leaving scars and internal feeding channels. Damage leads to wilting, stunted growth, and a compromised root. Applying diatomaceous earth around the base of the plant can help deter the adult flies from laying more eggs.
Wireworms are another subterranean pest, appearing as shiny, yellow-brown larvae that can live in the soil for several years. They damage turnips by girdling the stems or tunneling into the roots, which often results in the death of seedlings. Since mature wireworm populations are difficult to control once a crop is established, the best reactive measure is to remove and destroy severely infected plants to prevent further spread.
Managing Fungal and Bacterial Diseases
Clubroot, caused by the parasitic protist Plasmodiophora brassicae, is a serious soil-borne disease that affects the entire Brassica family. The most distinguishing symptom is the formation of swollen, distorted galls or “clubs” on the turnip roots, which prevents the plant from properly absorbing water and nutrients. Above-ground symptoms include yellowing, wilting during the day, and stunted growth.
Once clubroot is established, the only effective reactive measure is to immediately remove and destroy the infected plants. Amending the soil by incorporating lime to raise the pH level above 7.0 inhibits the pathogen’s spore germination.
Black rot is a bacterial disease caused by Xanthomonas campestris pv. campestris that often enters the plant through natural openings or small wounds. It is recognized by V-shaped yellow lesions that form on the leaf margins, extending inward along the veins. These veins eventually turn dark brown or black. Since there is no cure, controlling its spread involves removing and destroying infected plant material, ensuring good air circulation, and avoiding overhead watering when the foliage is wet.
Powdery mildew, a common fungal issue, appears as a white or grayish powdery growth on the leaves and stems. This growth reduces the plant’s ability to photosynthesize, causing leaves to yellow and die prematurely. Managing an active infection involves increasing air movement and treating with fungicides, such as those containing bicarbonate or sulfur, or horticultural oils like neem oil. Avoid applying oil-based treatments when temperatures are high, as this can damage the foliage.
Addressing Environmental and Soil-Related Problems
Turnip quality is highly susceptible to inconsistencies in temperature and moisture, which can lead to physiological disorders. Bolting refers to the plant prematurely sending up a flower stalk, shifting energy away from root development. This is often triggered by prolonged cool temperatures followed by sudden heat. Once a turnip bolts, the root becomes woody and unpalatable, so the best action is to harvest immediately. To prevent bolting, maintain consistent soil moisture and apply mulch to keep the soil temperature cooler during warmer periods.
Woody or bitter roots result from the turnip growing too slowly or being harvested too late, especially under heat stress or inconsistent watering. Lack of consistent moisture causes the plant to concentrate chemical compounds that create a sharp, bitter flavor and a tough, fibrous texture. The solution is to ensure a steady supply of water to promote rapid growth and to harvest the turnips promptly when they reach the desired size.
Root splitting, or cracking, occurs when a dry period is followed by a sudden, heavy influx of water, such as a downpour or heavy irrigation. The root absorbs the water quickly, causing the internal pressure to build up faster than the outer skin can expand, which results in a split. Preventing this issue requires maintaining a consistent soil moisture level throughout the turnip’s growth cycle, avoiding the extreme dry-to-wet fluctuations that stress the root.
A specific soil chemistry issue that affects turnip quality is boron deficiency, which manifests as internal browning or “water core” within the root. The internal tissue first appears glassy or water-soaked before turning brown or black and developing a punky texture. Turnips are highly sensitive to low boron levels, especially in alkaline or sandy soils, and the deficiency can be confirmed through a soil test. Correcting the issue involves amending the soil with a boron-containing fertilizer, often applied as borax, based on the soil test recommendations.
Long-Term Crop Health and Prevention Planning
Proactive planning is the most effective defense against turnip problems, beginning with careful site selection. Crop rotation is a foundational strategy, requiring that turnips or any other Brassica family crops not be planted in the same location for a minimum of three to four years. This extended break starves soil-borne pathogens and pests, such as Clubroot and Black Rot, which rely on host plants to complete their life cycles.
Before planting, a soil test provides information regarding nutrient levels and pH, informing preventative measures. Adjusting the soil pH to a slightly alkaline range (above 7.0) is highly effective in preventing Clubroot spores, which thrive in acidic environments. Ensuring the soil has adequate drainage and incorporating organic matter also helps prevent water-related stress and improves overall plant vigor.
Proper spacing and timing are simple cultural controls that reduce the likelihood of disease and bolting. Adequate spacing improves air circulation, helping foliage dry quickly and minimizing conditions favorable for fungal and bacterial diseases like Powdery Mildew and Black Rot. Planting at the correct time (early spring or late summer) allows the crop to mature during cooler periods, avoiding the heat stress that triggers premature bolting and woody roots.
Physical barriers, such as floating row covers, are a non-chemical method that prevents early-season insect pests from reaching young plants. When draped over the seedlings and sealed at the edges, these covers block adult flea beetles and root maggot flies from laying eggs. Selecting turnip varieties advertised as having resistance to common local issues, such as Clubroot or Black Rot, adds another layer of defense against potential crop failure.