actively remove or inactivate potential ice nucleating substances or accumulate natural antifreeze (e.g. glycerol or sugars) within their bodies. Some animals are also known to produce special proteins which inhibit the growth of ice crystals inside their cells. Freezing tolerance - here animals allow ice formation to occur, but generate ice nucleating proteins which help slow the speed and restrict the amount of ice produced, particularly inside cells. These animals can also stabilise their cellular proteins and membranes which help prevent ice damage. Most of our knowledge on the effects of freezing on invertebrate pests involves insects which use both tolerance and avoidance mechanisms to survive winter conditions. Nematodes are aquatic
organisms and, being in contact with water, are, therefore, much more susceptible to inoculative freezing (freezing in the soil water travels across the nematode body wall and ‘seeds’ ice formation inside the worm). This suggests that nematodes are more likely to use freezing tolerance mechanisms to survive the ice.
This appears to be the case with plant parasitic nematodes such as the stem nematode Ditylenchus and the foliar nematode Aphelenchoides. Freeze survival rates of juvenile Ditylenchus, are similar, whether or not the worms are in contact with water, and observations have confirmed that they are tolerant of cellular freezing. Some plant parasitic nematodes, such as cyst nematodes, overwinter in eggs which are further protected by the body wall of the female nematode (the cyst). Juvenile worms inside these eggs are desiccated and ice formation is restricted by both the cyst wall and egg shell.
It has been shown that, in some cyst nematode species, while hatched juveniles are quickly killed by ice formation, the eggshell can prevent inoculative freezing, allowing the unhatched worms to survive
temperatures as low as - 38O
C. It is not known how
widespread this protective mechanism is among plant parasitic nematodes, but it is likely that many species of nematode overwintering in eggs will be protected from freezing temperatures Another factor which may effect the survival rates of nematodes in freezing soil is the speed at which cold conditions appear. Root knot nematode juveniles show enhanced survival of sub-zero temperatures if they have been acclimatised to low temperatures before the onset of freezing. The slow onset of cold temperatures may allow the nematodes to “switch-on” protective mechanisms, while rapid freezing leaves the nematodes unprepared, resulting in much higher death rates.
Many nematodes have the ability to move in soil, and some species will be able to avoid freezing problems if they have migrated to, and inhabit, the deeper, warmer layers of a rootzone. Conversely, nematodes
exposed to freezing nearer the surface will experience higher levels of mortality. This also introduces a specific problem for sports fields which use under-soil heating systems. Here the nematodes will thrive in summer-like soil temperatures throughout the winter and population levels can continue to build up despite the cold weather. This may explain why some of the highest levels of plant parasitic nematodes are found in elite sports pitches with a high level of frost protection. Putting all this
information together suggests that significant numbers of insects and nematodes in our frozen greens and pitches will not have survived the big freeze. However, many pests, particularly those overwintering in eggs or cocoons, will be ready to hatch and start feeding as soon as soil temperatures rise in the spring. The actual severity of the winter mortality will only be apparent when we start to sample our turfgrass in the spring, and should we get a warm spring and summer, populations could soon be back at damaging levels.
• Reduces Nematode populations in sports grounds and golf courses
• Quick, clean and easy to apply • Economical - 1 litre treats 500m2
• Improves the look and quality of the grass
• Natural product - safe to use in public areas
ECOspray Limited
Grange Farm, Hilborough, Thetford Norfolk IP26 5BT United Kingdom
Tel: +44(0)1760 756100 /+44(0)7810 305605 Fax: +44(0)1760 756313
Email:
ecospray@ecospray.com
A juvenile cyst nematode in the egg is protected from freezing damage by its dessicated state, sugars acting as antifreeze and the eggshell
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