Root rot in chickpea
Phytophthora root rot (causal fungus: Phytophthora medicaginis)
This root-rot disease has the potential to cause serious losses and is widespread in southern Queensland. It is most prevalent under cool, wet conditions and waterlogged soils. The fungus survives in the soil for up to 3-4 years, and on other legume hosts, mainly lucerne and pasture medics. Phytophthora-infested soil can be spread by water and on machinery.
Infected plants usually occur in patches in low-lying areas of a paddock. Occasionally, individual plants over an entire paddock may be affected if the weather conditions are conducive, and there has been a previous history of the disease in the paddock. The lower leaves turn yellow, wilt and begin to die off. Below-ground the lateral roots will be rotted off, and later the taproot will decay and turn dark brown-black. Diseased plants can be easily pulled from the ground.
Assess the risk of phytophthora root rot prior to planting, based on previous paddock history, and select a variety with some resistance (Yorker, PBA HatTrick, Flipper, Jimbour, Kyabra and Moti have useful resistance) if there is any likelihood of this disease. Unlike Ascochyta blight there are no in-crop management options.
While the disease is usually observed late in the season, infection can occur from seed germination onwards if wet conditions are experienced after sowing. A fungicide seed dressing containing metalaxyl (i.e. Apron XL® and other products) can provide up to four weeks protection in the seedling crop.
Maintain a rotation of at least three years (and preferably four) between chickpea and lucerne crops, and medic pastures, to minimise the risk of phytophthora root rot.
Botrytis grey mould (causal fungus: Botrytis cinerea)
Grey mould can cause total crop failure. Crop losses are worst in wet seasons, particularly when crops develop very dense canopies. Early symptoms of the disease include flower abortion and failure to set pods. This can often go undetected unless the crop is closely monitored. Affected areas on the stem and leaf develop a soft rot and become covered in a fluffy grey mould. As the disease progresses, infected plants wither and die.
Avoid early plantings, high plant densities and narrow row spacings. The disease is also seed borne and can result in a substantial reduction in seedling establishment. Thiram-based fungicides are registered for the treatment of grey mould infected seed. While seed treatment can improve establishment, it does not provide any protection from air-borne infection later in the crop.
The disease can be controlled during flowering and podding with carbendazim or metiram based fungicides. Fungicide applications applied for the management of Ascochyta blight will also control stem and foliar grey mould. Consult your agronomist for the most appropriate fungicide for your situation.
Viral deseases in chickpea
Viral diseases
A number of insect-transmitted viruses can attack chickpeas, and can cause substantial crop losses. Symptoms include a reddening or yellowing of the foliage, a reduction in leaf size and twisting of shoots and tips.
Viral diseases tend to be very sporadic in Queensland and are largely influenced by seasonal conditions and proximity to broadleaf weeds and other crops (e.g. lucerne). Problems tend to be associated with high levels of insect, particularly aphid, activity.
Viral infections tend to be difficult to diagnose, and are often confused with nutrient deficiencies, herbicide damage, physiological disorders and waterlogging. Consult with your agronomist for further information. Several of these viral diseases are transmitted by seed (cucumber mosaic virus and alfalfa mosaic virus).
Control of broadleaf weeds on-farm will reduce the reservoirs for the viruses and insects. Planting into standing winter cereal stubble has been shown to reduce aphid activity in chickpea crops which can lead to a reduction in virus incidence.
Additional information can be found at Virus Control in Chickpea - special considerations (PDF 1.49 MB).
Environmental disorders
Physiological reddening
This condition is often prevalent in Amethyst crops. It occurs where the crop has been subjected to severe heat and moisture stress and then receives rain close to physiological maturity. Crops affected by this reddening often drop their leaves faster than normal.
Physiological leaf spot
This leaf symptom occurs regularly in most regions, and in most years. The spotting always appears on the upper leaf surface, and is brownish in colour. No disease pathogens have been linked to this condition, which appears to be associated more with stress conditions on the crop.
Root lesion nematodes: (mainly Pratylenchus thornei)
Nematodes are minute, worm-like parasites that attack the root system of susceptible crops. They are usually less than 1 mm long. The most obvious symptom of nematode damage is patchy, uneven crop development. Approximately 70% of the wheat-based farming country in southern Queensland is infested to varying degrees with root-lesion nematodes (RLN). In paddocks with moderate nematode numbers, relatively susceptible varieties such as Amethyst or Sona can suffer up to a 15-30% yield loss, whereas more tolerant varieties like Jimbour might suffer a 5-10% yield loss. Soil test levels above 2000 nematodes/kg of soil are likely to impact on chickpea yields (based on 0-30 cm soil sampling).
Nematode numbers will also build up on the root system of chickpeas. The extent that RLN numbers build up on the crop root system (resistance), may impact on subsequent crops in the rotation. Nematode build-up on chickpeas is similar to that on other susceptible hosts (barley, maize and triticale), but much less than on susceptible wheat varieties (less than 50%).
Fungicide registrations
Table 2: Fungicides currently registered for chickpea (as of May 2010)
