Poppy Cultivation in Australia: Plant Diseases

2014

Although a number of fungal diseases of poppies which can have an impact on morphine concentration and yield have been recorded in Tasmania, their incidence has generally been low and fungicides are not commonly applied. These diseases have included poppy fire (Pleospora papaveraceae), Sclerotinia wilt (Sclerotinia sclerotiorum) and poppy leaf smut (Entyloma fuscum).

In exceptional seasons the morphine concentration of capsules has been reduced to about half the normal average. The fungi involved on this occasion were identified as Dendryphion penicillatum (Corda) Fr. the conidial stage of Pleospora papaveraceae, Alternaria alternata (Fr.) Keissler, Cladosporium macrocarpon and Stemphyllium vesicarium (Laughlin and Munro, 1982). In these field and laboratory experiments, associations were drawn between the degree of fungal cover of the capsules and their morphine concentration. The morphine concentration of capsules which had been colonized by fungi to the extent of >30% of their surface area were 20% lower in morphine than those capsules with a light fungal colonisation of <10%. The colonisation of these capsules was generally localized in the top half and the morphine concentration of the top half was about 20% less than the bottom half. In contrast, glasshouse-grown capsules which were free of fungal colonisation had similar morphine concentrations in the top and bottom halves of each capsule (). These associations between fungal colonisation and morphine concentration were similar to those found in European poppy growing areas in Poland. In the Polish study (), the morphine concentration of capsules was inversely proportional to fungal cover with a reduction of 50% morphine in capsules with more than a 50% cover of fungi.

In the field studies of Laughlin and Munro (1982) the development of fungal colonisation was often related to capsule tissue which had suffered physical damage and often to the removal of the waxy bloom which covers intact capsules (). This damage and the removal of surface wax is often caused when capsules are chafed by the sharp stigmatic discs of neighbouring capsules but can also be a result of the abrasive effect of wind-blown sand and dust () and rain. In addition to allowing fungal colonisation, the removal of wax from the surface of capsules also facilitates the loss of morphine by leaching (). In other Tasmanian studies, Hoffman and Menary (1984) also showed that losses of capsule codeine and thebaine were aggravated by loss of the surface wax from capsules.

Sclerotinia sclerotiorum

Sclerotinia stem infection by Sclerotinia sclerotiorum (Lib.) de Bary can occur relatively frequently with poppies in Tasmania. Although this infection does not cause any overall reduction in morphine levels in capsules it can weaken the stem and make the plants more susceptible to lodging by wind. The typical symptoms of infection by S. sckrotiorum are that lesions with concentric dark and light zoned areas appear on the surface of the main stem in the lower third of the plant, most typically at the point of attachment of a senescent leaf. Later, the infected area of the stem shows a bleached appearance. Less commonly, lateral branches may show the same symptoms and on rare occasions the capsules may also be infected. The incidence of Sclerotinia stem infection and its effects on the dry matter and morphine production of poppies were assessed in a field experiment on krasnozem soil at Forthside (). Sclerotinia had the effect of redistributing morphine within the plant but did not cause any reduction in total plant morphine. The concentration of morphine in terminal capsules was reduced by about 13% compared with non-infected plants but the concentration in lateral capsules was increased by a comparable amount and there were no effects in capsule dry matter. Similarly, there were no effects of Sclerotinia on the dry matter yield of stem and leaves but there was a marked increase of 75% in the morphine concentration of stem and leaves. This redistribution of morphine within the plant was interpreted as a disruption of normal translocation of morphine by the latex vessels to the terminal capsules. The effect on lateral capsules was further interpreted as the influence of Sclerotinia, altering the normal apical dominance within the plant so that lateral rather than terminal capsules became the main sink for morphine ().

Although Sclerotinia infection does not appear to affect morphine production of poppies, there are practical considerations other than the effect on plant lodging which should be considered. In Tasmania, poppies are often grown as part of a rotation which includes a range of processing vegetables of which green beans (Phaseolus vulgaris) are particularly susceptible to Sclerotinia. The position in which poppies are placed in the rotation should be carefully considered as a means of controlling Sclerotinia in subsequent vegetable crops.

Entyloma fuscum

Poppy leaf smut (Entyloma fuscum) has appeared periodically in Tasmanian poppy crops and can be controlled by the application of propiconazole and chlorothalonil. Light infections of poppy leaf smut are not considered to significantly affect crop production in Tasmania. However, severe infection early in the growing season with premature defoliation may have very adverse effects on yield. The effects of partial and complete defoliation simulating Entyloma damage at various stages of plant development were studied in a field experiment on krasnozem soil at Forthside (). Complete defoliation at the hook and full bloom stages had drastic effects on capsule and morphine yields and the photosynthetic capacity of the stem did little to sustain growth. Complete defoliation at the hook stage reduced capsule yield and morphine concentration at dry harvest maturity by 86% and 50% less than nondefoliated plants respectively. The comparable reductions from complete defoliation at full bloom were 51% and 25% respectively. Complete defoliation at maximum volume of green capsules (two weeks after full bloom) had little effect on capsule yield or morphine concentration. Partial defoliation of either top or bottom leaves at the hook or full bloom stages resulted in a 25% reduction in capsule and seed yields at dry maturity, but had no effect on capsule morphine concentration. Detailed symptoms of Entyloma infection in poppies and weed poppies in Tasmania have been recorded ().

Insect Pests

Insect pests of poppies are not a major problem in Tasmania. There have been sporadic infestations of springtails (Collembola sp.) which can defoliate very young seedling plants on occasions. Spraying with methoate has been shown to be effective but this operation is only carried out routinely by a minority of growers. In some seasons in Tasmania damage to seedling poppy crops which had initially been attributed to insect pests was ultimately revealed to be caused by the European Skylark (Alauda arvensis). Damage caused by the European Skylark has been quite serious in some autumn-sown crops.

Native bud worm (Heliothis punctigera) is also an occasional poppy pest in Tasmania and damage usually occurs from the green capsule stage to the time of dry commercial harvest. A typical symptom of native bud worm attack is a small round hole in the capsule wall. The net result is a relatively small decrease in capsule yield but, more importantly, a more significant loss of seed. Insecticides can only be effectively applied by aerial spraying for this particular pest but this is rarely necessary or used.