Broom's Barn Applied Crop Sciences

Other problems affecting sugar-beet roots

Pests

	Soil pests attack from the earliest growth stages. They can kill young seedlings and severely stunt the growth of plants that survive their damage. The younger the plant the more vulnerable it is, and the larger the pest the more damage it can do. Pests such as wireworms, leatherjackets, millepedes and slugs can easily sever the tap root of a young seedling. However, what small pests such as pygmy beetles and springtails lack in size, they often make up for in population. Black pits on the tap root and, in the case of smaller pests, on the lateral roots are a typical symptom of soil pest attack. Larger soil pests tend to make larger pits. The small pits in the picture were made by pygmy beetles. It is usually difficult to determine the pest responsible from the damage, and searching for the pest in the soil is a better method. For smaller pests it may be worth putting some soil into water and examining the creatures that float to the surface.
	On lighter soils, free living nematodes (so called because they live freely in the soil and do not invade the plants they feed on) may be numerous and set back growth of plants considerably. When stubby root nematodes (Trichodorus species) and needle nematodes (Longidorus species) feed on the lateral roots, these then cease to develop and become short and stubby. Early attack may also affect the growth of the tap root causing it to become fangy. (The picture is of Longidorus damage). Free living nematodes cause more damage in wet springs because they can move more freely within the soil. They can attack a wide range of plants, and hence are not controlled by rotation. The damage in the field typically shows a 'chicken and hen' effect i.e. larger plants mixed with smaller ones. It may be widespread in a field, rarely in well defined patches.
	Beet cyst nematode is more likely to be a problem on close rotations. The nematode invades the root tissue and from June onwards white cysts (female nematodes swollen with eggs) appear on the roots. The cysts are visible with the naked eye but are more easily seen on plants grown in, say, black fen soil than in soil with numerous light-coloured sand particles. Severely infested plants are stunted and often have a profusion of lateral roots (see picture). The damage typically occurs in a patch.
	The picture is of swellings produced by root knot nematode. This pest is controlled effectively by crop rotation and its damage is much less common than that by free-living or cyst nematodes. The swellings are galls produced by the plant as the adult female nematode grows inside the root tissue.

Weather

	In the spring frost scorches the foliage and stems of seedlings. Sometimes the stems of young seedlings become blackened due to a layer of frost on the soil surface. Some seedlings die because the stem is severed. Frost causes damage too at the end of the growing season. Tap roots, either in clamps or in the ground, can freeze. The cell walls rupture, allowing pathogenic fungi and bacteria to invade. Once frozen, roots should be delivered to the factory as soon as possible because they cannot be processed when they start to deteriorate after thawing.
	A lightning strike in a sugar beet field will result in a patch of sick and dying plants. Those that receive a direct hit, in the centre of the patch, will be the worst affected. The roots will be largely blackened and the foliage scorched. Even those not hit directly may be badly affected because the lightning heats the water in the soil and the roots are boiled alive. In such a case the lower part of the tap root dies, and eventually rots away (see picture). The upper part of the tap root may survive if it sends out lateral roots that then reach and remain in moist soil.
	Strangles, a distinct constriction of the tap root at the soil surface, has more than one cause. Sometimes buffeting by the wind alone can result in the tap root becoming abraded at the soil surface. The root becomes increasingly thinner at this point and may eventually snap in two. However, the initial cause of strangles may be disease (e.g. blackleg) or pest damage.
	Following very wet weather tap roots shaped like the one in the picture may develop. The tap root is rounded instead of pointed, and the lateral roots point out to the side or even up towards the soil surface. This effect is due to waterlogging, which produces a layer in the soil that the roots cannot penetrate. Similar effects can occur in compacted soil. In fact the two problems often go hand in hand. Compacted soil is more likely to become waterlogged, and waterlogged soil tends to consolidate.

Herbicides

The symptoms of damage by herbicides to root systems vary. Some types of herbicide may cause the tap roots to develop short stubby lateral roots like those in the picture.

Dinitroaniline herbicide residues may produce spiral tap roots, sometimes with a distinct constriction ('deep strangles').

Residues of sulphonyl urea herbicides sometimes produce unhealthy-looking underdeveloped root systems.