Bean Seed Fly
In recent years poor germination of beans, and sometimes peas, has become an increasing problem and samples returned by customers have shown that this fly is very often responsible. The larvae of this pest, which are small white maggots, attack the growing point and seed leaves of the bean as it attempts to germinate. If these attacks don’t kill the bean then fungal rots which follow them often do and, in many cases, the seedlings don’t emerge from the ground.
Problems of this kind are most likely when beans are struggling to germinate in cold soil and are much less often seen when they are sown under glass of if sowing outside is delayed until a spell of warm weather has thoroughly warmed the ground. Attacks can also be prevented by a dressing of soil insecticide raked in before sowing.
Certain birds can be very damaging to some seedlings, particularly brassicas, which are very prone to damage from pigeons. Where birds are troublesome, covering rows or beds with a fine mesh net raised a few inches off the ground will give good protection.
Carrot fly (Chamaepsila rosae) is a small black fly which lays its eggs around the roots of carrots. After hatching, the fly's larvae burrow into the carrot's roots, leaving scarred rusty coloured tunnels. Affected crops will often suffer from wilted tops and stunted roots. Carrot flies may also affect celery, celeriac and parsnips.
Sowing carrots after mid-May when the flies first lay their eggs will help avoid infestation, as will growing crops which harvest before late August, when the fly produces a second generation.
Carrot flies locate places to lay their eggs using smell, so sowing carrots carefully in order to avoid the need to thin the crop, or using a seed tape which contains optimally spaced seeds may help. Planting carrots between rows of onions can also be beneficial, as the scent from the onions can help mask that of the carrots.
Carrot flies are said to be incapable of flying more than 2 feet (60cm) from the ground, so growing in tall raised beds, or screening with polythene around the crop up to this height can stop flies from reaching the crop. Alternatively, ground grown crops can be protected with Enviromesh, which prevents carrot fly reaching the crop, whilst still allowing light and moisture to reach the ground.
Cats and Dogs
Freshly made seedbeds are extremely attractive to these pets, particularly cats. Commonly their excavations will bury some seeds too deeply, expose others on the surface where they dry out and move still others to where they are not wanted. Young seedlings can be similarly buried or uprooted and the overall result can be large gaps and seedlings appearing all over the place rather than in the intended rows.
Various repellent chemicals and ultrasonic repellent devices are widely sold but, in our opinion, the best method of preventing this kind of damage is to cover beds or rows with netting or chicken wire. Covering with cloches or fleece has a similar effect.
These are not worms but the caterpillars of certain moths which live in the surface layers of the soil and eat through the stems of seedlings at soil level. If they work their way along a row they can cause considerable damage. They are usually only a problem in the garden where control can be achieved by dusting drills with a soil insecticide when sowing. Where use of chemicals is not desired or if damage still occurs, a careful search of the soil near the damaged plants will often reveal the culprit.
These rodents are also very partial to pea and bean seeds and can quickly clear out a whole row, again making it appear as if germination has failed. Where mice are known to be troublesome an old remedy is to dip pea seeds in paraffin before sowing while beans can be raised under glass. Alternatively, careful baiting or trapping may need to be considered.
Slugs and Snails
These pests love the soft, juicy seedlings of many plants and will seek them out. A whole row of newly germinated cabbages or pot full of young lettuce can mysteriously disappear overnight if a large snail finds them. Problems are most acute in the garden but slugs, in particular, also enjoy conditions in the greenhouse and can cause much damage there too.
Various chemical baits and poisons are widely available but many must be used with care, as some are toxic to pets or wild animals which feed on slugs and snails. Safer control can be carried out using traps, such as those containing diluted beer and set slightly above soil level, which will drown or collect many slugs which can be subsequently disposed of, or nematodes.
Nematodes are naturally occuring parasitic organisms which live in the soil and feed on other creatures. Nematodes which feed solely on slugs, such as those marketed as Nemaslug are applied to the soil in a solution applied with a watering can. Once applied, they'll continue to kill slugs for a number of weeks after which the number of nematodes will fall back to a naturally sustainable level. Plant damage can also be prevented by using barriers around plants, such as Slug Gone, which is formed naturally from wool and irritant to slugs and snails. In the greenhouse, good hygiene, particularly measures which reduce places where slugs and snails can hide during the day, will usually keep them under control.