Turnip yellow refers to a plant disease impacting turnips and other related brassica crops, such as cabbage, cauliflower, broccoli, and oilseed rape. This condition poses a challenge for both home gardeners and commercial growers, potentially leading to reduced yields and overall crop quality. Understanding its characteristics and spread is an important step in mitigating its effects on susceptible plants.
Recognizing Turnip Yellow
Turnip yellow causes distinct visible symptoms on plant leaves. A common sign is interveinal yellowing, where the areas between veins turn yellow while veins remain green.
This yellowing can sometimes be accompanied by a red or purpling discoloration along the leaf margins. Affected plants may exhibit stunted growth, with early infection leading to more pronounced stunting. Leaf distortion, such as mottling or the development of bright yellow and dark green mosaic patterns, can also occur, particularly in crops like Chinese cabbage. These symptoms can often be mistaken for nutrient deficiencies, frost damage, or other forms of plant stress.
The Viral Culprit and Its Spread
Turnip yellow is caused by the Turnip Yellow Mosaic Virus (TYMV). This virus primarily affects plants within the Brassica genus. Once a plant is infected with TYMV, it cannot be cured.
The primary way TYMV spreads is through insect vectors, especially aphids, which are significant carriers. These aphids acquire the virus by feeding on infected host plants, including oilseed rape, other brassica types, lettuce, and certain weed species. The virus can then be transmitted to healthy plants as the infected aphids move and feed. While aphid transmission is the main mode, mechanical transmission, such as through contaminated equipment or hands, can also occur. The virus can also overwinter in perennial weeds and self-sown crops, serving as reservoirs for future infections.
Strategies for Management
Since there is no cure for viral plant diseases like turnip yellow, management focuses on preventive measures and limiting spread. Removing infected plants, a practice known as roguing, helps reduce the source of the virus in the garden. Practicing crop rotation, especially with cereal crops, can help break the disease cycle and reduce the build-up of the virus in the soil.
Controlling weeds is another important strategy, as many common weed species can harbor the virus or its aphid vectors. Physical barriers, such as row covers, can protect against insect pests like flea beetles, which are vectors for TYMV. For larger scales, insecticide-treated seeds can prevent early aphid colonization and reduce virus infection.
Using certified, healthy seeds or transplants is also a sound practice to avoid introducing the virus into your garden. While broad resistance to TYMV is still being developed, some commercial varieties of oilseed rape and Danish cabbage may offer resistance.