A Technical Guide for Wine Producers

RECENT ARTICLES   |   WYNBOER HOME THE IMPORTANCE OF SOIL AND BUD ANALYSES FOR VINEYARD AND ORCHARD PESTS IN INTEGRATED PEST MANAGEMENT Pia Ueckermann & Hans Hugo, ARC - Fruit, Vine and Wine Research Institute, Stellenbosch With the current focus on Integrated Pest Management (IPM), monitoring for pests and diseases plays an important role in the management of vineyards and orchards. Nematodes, phylloxera and grapevine bud mites are not visible to the naked eye and visual sampling is unreliable, since occurring symptoms can have many causes and are not specific for these pests. Soil and bud analyses are the only effective methods to determine whether these pests are present at levels which warrant chemical control. The accuracy of analyses depends greatly on the way in which a sample is taken, and it is therefore important to follow specific guidelines. SAMPLING FOR GRAPEVINE BUD MITE The first indications of bud mite presence are deformed leaves and bunches, shortened or zig-zagged internodes and witches=-broom growth, which all occur shortly after bud burst. In severe cases the buds may also die. To assess whether a spray programme is necessary, dormant buds where the mites are found for most of the year should be examined microscopically. Certain cultivars are more susceptible than others and regular sampling of the following is therefore recommended: WINE GRAPES TABLE GRAPES DRIED GRAPES Cabernet sauvignon Dauphine Muscat d' Alexandrie Fernao pires Dan-ben-Hannah Sultanina Frans Muscat d' Alexandrie   Muscat d' Alexandrie Sultanina   Sultanina Waltham Cross   Procedure: Mites reach their highest levels after leaf drop, therefore samples should be taken during this period until bud burst. No pruning samples should be submitted for examination as mites are mostly concentrated on the lower bud positions. Collect sixteen canes from different vines systematically throughout the vineyard. The first eight basal buds on all canes must be included. Clearly mark samples with the block number and cultivar, date, name, postal address and telephone number of the contact person to whom results should be sent. Wrap samples in plastic to prevent drying out. If samples cannot be delivered immediately, they should be refrigerated or kept as cool as possible until delivery. Results of analyses will state the percentage damaging infestation and dead buds and a recommendation for control will be given. Dead buds could be the result of a high bud mite infestation, but can also have other causes, such as incorrect use of Dormex, phytotoxicity caused by certain herbicides and boron deficiency. If an infestation exceeds 30%, a standard bud mite spray programme can be followed as some economic damage can be expected at this level. To minimise the danger of resistance developing against miticides, chemical sprays are not recommended at infestations lower than 30%, or if an analysis has not been performed. SAMPLING FOR NEMATODES AND PHYLLOXERA Nematodes and phylloxera attack the new growth of roots and commonly lead to poor growth and general deterioration of vines and fruit trees. Phylloxera primarily occur on the roots of vines, but can sometimes be found to infest vine leaves. Root-knot nematodes form small round galls on the roots, whereas galls caused by the dagger nematode and phylloxera are more hook-like in appearance. Ring, lesion and stubby-root nematodes don't cause obvious visual symptoms on roots and their presence can only be determined by a soil analysis. Decline of the crop due to these pests usually occurs in patches and is similar to decline caused by soil-borne diseases. Since various factors, such as soil type, age of crop and rootstock-type, need to be taken into consideration when determining the damaging potential of nematodes and phylloxera, both soil and root analyses are important. Procedure for nematode sampling in planted soil: 12 - 15 soil cores/ha must be collected systematically throughout the vineyard to make up approximately 1kg of soil. Fine feeder roots must be included in the sample for a root analysis. It is recommended that two soil samples be taken, one in the area of poor growth and one in soil where growth is good. The latter can be used as a control sample. This often helps to determine if nematodes are the primary cause of a problem. Soil cores taken from vineyards must be taken within 30 cm of the vine stem at a depth of 30 - 40 cm or in the major root zone. Soil cores taken from fruit orchards must be taken under the tree canopy approximately 50 cm away from the tree trunk, at a depth of 10 - 30 cm. Soil samples must not be too wet or too dry, and must be placed in sealed plastic bags, clearly marked with the cultivar, rootstock, block number, age of the crop as well as the name, postal address and telephone number of the contact person to whom results should be sent. Soil samples can be taken throughout the year, but the best periods are during active root growth (around harvest and bud burst). Procedure for nematode sampling in bare soil: Sampling for nematodes in soil where no crop is planted is not recommended. If the previous crop has recently been taken out and the soil still contains moisture and roots, an analysis can still be done but results could be misleading, giving an inaccurate reflection of possible damaging numbers. If vine or fruit tree roots are not present anymore, the sample should be taken around any weed roots still growing in the soil. Samples should be taken after rain and the first 10 cm of soil should be discarded. In situations where the soil is bare and dry, nematodes will survive in the deeper layers of soil, often in a dormant phase or egg stage that cannot be identified through a soil analysis. Nematodes can survive such conditions for a few years, but determining their pest status at this stage is not possible. It takes at least two years for nematodes to decline in numbers, but they will never disappear completely. Once a suitable host is planted, their numbers will again increase. Results of analyses will state the level of infestation (low to severe) of plant-parasitic nematode genera present and a recommendation will be made taking all factors into consideration. The producer can then make a more accurate decision on the implementation of a control strategy based on these results. The age of the crop is important as this affects the success of possible treatments. Depending on the severity of the infestation, it is unlikely that older vines or trees will ever recover. Procedure for phylloxera sampling: The best time to sample for phylloxera is during summer. A handful of fine feeder roots taken from 5 - 10 vines are necessary. If the roots become dry or are left out of the ground too long, the phylloxera could drop off. Roots should be placed in a small amount of soil with the minimum amount of handling and kept cool. The sample should be delivered as soon as possible after being collected. No chemical treatment is currently registered for the control of this pest. The only method of limiting the occurrence of phylloxera is through the use of resistant rootstocks, such as Richter 99 or 110. Following the correct sampling procedure will ensure that producers receive more accurate results and recommendations. For further information contact Pia Ueckermann (vine samples) at telephone number (021) 809 3145, fax number (021) 809 3002 or e-mail: piau@nietvoor.agric.za; or Hans Hugo (deciduous fruit samples) at telephone number (021) 809 3468, fax number (021) 3400 or e-mail: hans@infruit.agric.za.

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