CRUCIFEROUS VEGETABLES - DISORDERS
Physiological lesions are symptoms that can be localised by the elimination of physical impact, but are easily confused with pathological, and insect-caused symptoms. It is important that growers learn to identify these symptoms as they cannot be treated with chemicals.
EDEMA
Edema is often expressed as off-color swellings or galls that appear on leaves and stems. Edema develops when epidermal cells hold excessive water due to a slowing of evapotransporation when hot, muggy days are followed by cooler, wetter weather. Edema develops because the plant takes in more water (due to a high soil moisture content) faster than can be eliminated by evapotranspiration, causing cells to rupture, results in blistering of the leaves. Edema is strictly caused by environmental factors and can appear whenever these conditions occur.
29. Figure: Edema on cabbage leaf
Symptoms: May affect any plant part, but usually occur on lower leaf surfaces. First symptoms are watery blisters or galls, many or just a few. More succulent tissues are more susceptible. Blisters or galls turn dark brown, yellow, or rust-coloured and give the appearance of a rust or bacterial infection.
Control: Properly monitor soil conditions, irrigation cycles, and the weather, to avoid over irrigating on warm or hot early spring days, especially when cold fronts/ abrupt temperature drops and cloudy weather are expected.
- Control insects, particularly aphids and thrips.
- When cabbages are small, control windblown soil particles by sprinkler irrigation when winds are high.
- Harvest storage varieties before the onset of heavy autumn rains, which waterlog the soil.
- Varieties differ in susceptibility, so it is good insurance to grow several suitable varieties rather than just one or two.
- Damaged heads often can be salvaged by stripping off outer leaves, which are most severely affected. This makes economic sense only if the market is particularly strong.
HOLLOW STEM
Hollow stem is a physiological disorder in cabbage, cauliflower and broccoli - frequently linked to calcium and boron deficiency or over-supply of nitrogen.
Boron deficiency can increase the likelihood of hollow stem in broccoli, which causes small gaps in the stem tissues that enlarge over time to cause a large hollow spot in the stems. Plant spacing and nitrogen fertilization also impact the likelihood of this disorder.
Control: Boron addition by phenology
30. Figure: Broccoli hollow steam
LEAF EDGE BROWNING
Calcium deficiency can cause a disorder called tipburn, characterized by a breakdown of tissues within heads of cabbage, sprouts of Brussels sprout, and inner leaves of cauliflower.
31. Figure: Calcium deficiency on cabbage leaf
Molybdenum deficiency can cause a disorder caused whiptail in broccoli, cauliflower and Brussels sprouts that manifests as a malformation and stunting of the leaf surface so the leaf is reduced down to mainly the mid-rib, giving it a whip-like appearance.
32. Figure: Molybdenum deficiency
Control: If deficiency symptoms are suspected, contact your crop or soil fertility specialist for diagnostic services (soil or plant tissue analysis may be needed).
Climatic Limitations When some Brassica varieties are exposed to cool temperatures (5-10°C) for prolonged periods (10 days) early in their development, they may undergo early flowering or bolting, which causes plants to flower well before they have reached a vegetative size capable of producing a marketable flowering head. Care must be taken when hardening transplants for the field, as bolting may be induced by both insufficient hardening and rapid reductions in temperature.
- TURNIP MOSAIC VIRUS (TUMV), CAULIFLOWER MOSAIC VIRUS (CAMV), TURNIP YELLOW MOSAIC VIRUS (TYMV).
- BACTERIAL LEAF SPOT OF CABBAGE
- BACTERIAL SOFT ROT
- BLACK ROT
For more information on the bacterium, follow this link.
- DAMPING OFF 10 DOWNY MILDEW
- ALTERNARIA LEAF SPOT
- VERTICILLIUM WILT
- BLACK LEG
- CLUBROOT
For more information on fungi, follow this link.
- EDEMA
- HOLLOW STEM
- LEAF EDGE BROWNING 19
For more information on disorders, follow this link.
- FLEA BEETLES
- CABBAGE ROOT FLY
- CABBAGE APHID
- LARGE AND SMALL WHITE BUTTERFLIES
- MOTHS
- DIAMONDBACK MOTH
- ONION THRIPS
- WEEVILS
- CABBAGE CROWNGALL FLY (SWEDE MIDGE)
- TURNIP SAWFLY
- CABBAGE WHITEFLYFor more information on insects, follow this link.