Poppy germinates and comes up within 10-14 days of sowing. During this period cracking of the soil surface may severely hamper or even stop this process and thus soils liable to cracking have to be loosened regularly. In early spring in the case of the winter poppy, rolling with a light roller is necessary if the soil structure of the plantation is frost damaged.
If the plantation is set up using traditional methods, the poppy stand should be thinned when the plants are at the 4-6 leaf stage. On smaller fields or in high-density stands thinning has to be repeated twice (at the 2-3 leaf and 5-6 leaf phases), but this procedure requires a lot of labour and costs can reach a third of the whole production expenses ().
Plant Density and Thinning
The optimum plant density should be reached in order to get optimal yields. Plants at a distance of 3-4cm apart are capable of developing one capsule per plant, but those spaced 10-20cm apart may produce 3-4 capsules; higher capsule numbers per plant are, however, dependent on many other climatic and agro-technical factors. Muchova et al. () proved that a significant positive correlation exists to a certain extent between seed yield and the number of plants per unit area. The optimal plant separation can be determined according to the cultivar characteristics and the harvesting method. In cases where combine harvesters are used, a uniform plant height is required; this can be achieved by using a higher plant density but this also results in lower capsule numbers per individual.
Special machines to mechanize thinning have been proposed but their use is thought unlikely to become widespread because their effectiveness is uncertain in the diverse ecological and biological circumstances of poppy cultivation in the temperate zone ().
In the 1950s and 1960s thinning was attempted by harrowing the rows in cross directions and experiments using specially designed machines were also carried out to reach this aim. According to Bulgarian practice, the optimal width of the strips proved to be 15-16cm (). However, this technology was not able to produce optimal plant densities and yields hardly exceeded those obtained without thinning. Another method, applied in Hungary, was thinning the poppy stand by spraying with a herbicidal preparation (). Plants were killed off in 15cm wide strips. According to further experiments the two above mentioned methods could be applied in parallel (). However, by using these thinning methods small bunches of plants still remained, the utilization of space by the plants was not optimal and some manual work was required afterwards to manage the proper plant standing.
Winter poppy crops are thinned later on in their development stage than the spring types. They are thinned at the 6-8 leaf stage which is only reached in spring, depending on geographical region, e.g. in Hungary it is during the second half of March and in Bulgaria it is February or the beginning of March.
Irrigation may be necessary on very loose soils or regions where precipitation levels are extremely low during sprouting, at development of the leaf rosette and at budding. According to Shulgjin () the usual quantity of water used is 800m3/ha, which should be applied when the soil moisture content falls below 70%. In southern European conditions, e.g. in Bulgaria, spring-sown poppy is irrigated regularly — three or four irrigations are recommended in the phases of leaf rosette and stem development and in the budding stage; however the amount of water used per irrigation is much lower than that mentioned above (300-400m3/ha). The usual method in these areas is furrow irrigation. However, the majority of poppy cultivation in the temperate zone is managed without irrigation or it is only applied in extremely dry years because of economic considerations.
Under irrigated conditions top-dressings of about 20kg/ha nitrogen (ammonium-nitrate) in the phases of rosette formation and budding and 20kg/ha magnesium chlorate at the start of flowering have been proven to be beneficial ()
Poppy: Weed Control
The growth of poppy is very slow in the early stages and the small plants are unable to compete with weeds. After germination, when rows become visible the weeds should be removed by hoeing. By using only mechanical methods, weeding may be needed three to five times during the vegetation period or even until the budding — flowering period.
In large-scale cultivation effective weed control is one of the most important elements of cultivation technology. Weed control in these conditions is based on herbicides, although poppy is rather sensitive to these chemicals. Experience has shown that effective weed control cannot be based solely on preparations which have long-term effectiveness — complex technology is necessitated, which depends on the development of the poppy plants, the spectrum and density of weeds and weather conditions.
Herbicide control begins within three days of sowing. For pre-emergent treatment until the last stages of development nitrofene (8-101/ha) was the most widely used agent, but its effect only lasts for a few weeks and is strongly dependent on the weather. Recently, chlortoluron (1.0-1.5kg/ha) can be mentioned as the most frequently used herbicide at this stage of poppy growth, but several other materials have also appeared, e.g imidasolin (0.3-0.41/ha), nitrofen, buminafos (). This treatment should ensure a clean stand for 4-6 weeks.
If strong or resistant weeds develop during this period, diquat (2.5-31/ha) spraying may be necessary and this destroys the weeds by singeing the leaves. The application of diquat is possible when the poppy has at least 2-4 leaves until the 8-10 leaves has formed. The aim of this treatment is to keep the plantation weed-free from the first pre-emergent herbicide application until the time of the second post-emergent treatment.
The second post-emergent herbicide application may be carried out after the poppy plants have developed at least 8-10 leaves when several different compounds are applicable. The aim of the second post-emergent herbicide treatment is to kill existing weeds and prevent the further germination of both monocotyledon and dicotyledon species. The application of chlortoluron is very commonly used to reach this goal in 2 kg/ha doses. The utilization of many other compounds have been reported: pyridate (3-4 kg/ha), fluroxipir (1-1.21/ha) or fluazitop-butyl against monocotyledonous weed species (); and diclotop-methyl, flamprop-isopropyl (). Combinations of chlortoluron+asulum (8-101/ha) and chlortoluron+metolachlor (1.5-2kg/ha) preparations are also applicable according to the weed spectrum, and can give a better result than single chemicals (). The poppy stand can be treated with appropriate herbicides during the whole vegetation period, even in the budding and flowering stages, when the tolerance of the poppy increases more quickly than that of some dangerous weed species, e.g. Chenopodium, Amaranthus (). However, such a late treatment seems to be necessary only if the large amount of weeds endangers the harvesting process.
In the case of the winter poppy a post-emergent treatment is generally necessary in the spring. This can be repeated once, but the fallen weed leaves usually cover the soil quickly, preventing further weeding by acting as a mulch (). The same chemicals as those applied to spring-sown crops can be used.
At the application of herbicides, the slight singeing seen on poppy plants does not usually cause a decrease in the yield. Damage to plants can be minimized by lowering the drop size of the spray to 250-300um and increasing the volume used to 300-600 1/ ha. The occurrence of singeing is more frequent in rainy conditions which tend to thin the waxy layer of the leaves. The waxy layer begins to thicken 3-4 days after rain, so further herbicide application is beneficial.
In herbicide technology, pre-emergent treatments are the most important, while post-emergent applications are often substituted by manual work.
Herbicides may not be combined with insecticides or fungicides, which have a different action. If mechanical weed control is also undertaken, the condition of the plants must be considered carefully because damaged leaves are more susceptible to harm from herbicides.
Weed control is thus a crucial component of cultivation technology. If it is not performed correctly the crop may be spoiled and harvest may have to occur at a non-optimal time and in a non-optimal manner; infection by fungi may also increase and seeds and capsules cannot be harvested and cleaned afterwards.
Selections from the book: “Poppy. The Genus Papaver”. Edited by Jeno Bernáth. Series: “Medicinal and Aromatic Plants — Industrial Profiles”. 1998.