Small bugloss is an annual spring or winter weed from the dicotyledon class, which germinates mainly in spring, early summer, and autumn.

A characteristic feature of this species is the rough, bristly hair on the upper side of the leaves, as well as the stiff and prickly hair covering the entire plant.

It has a branched root system. The stem is 15 to 45 cm high, round, erect, may be branched, with prickly, protruding hairs. Cotyledons are elliptical, 10 to 13 mm long, broad, tapering bluntly at the top and wedge-shaped at the base, green, rough and bristly on top, smooth underneath. True leaves are lanceolate with wavy edges, entire or finely serrated; upper leaves are heart-shaped, nearly sessile, and lower leaves are petiolate. The inflorescence is a leafy scorpioid cyme, composed of light blue flowers, with a white, bent corolla tube underneath, on a short pedicel. The fruit is a nutlet shaped like a little shoe, rounded at the top, finely tubercled, gray or dark brown. Seeds are elongated and gray in color.

Occurrence and harmfulness

Small bugloss occurs in root crops, cereals, and fallow lands. It grows on light, sandy, moderately moist, acidic soils, but also on calcareous soils.

Its harmfulness is due to rapid seed dispersal and soil infestation, and it also serves as an intermediate host for brown rust of rye.

Control

Mechanical method

The long period from planting to potato emergence is a critical phase (ideal conditions for weed development) that can be used for mechanical treatments. These are carried out using available farm machinery, e.g., hilling machines, light harrows, finger weeders, etc. Their main task is to create the most favorable conditions for rapid weed germination, followed by destruction through subsequent cultivation operations. Maximum efficiency (even over 90%) can be achieved when weeds are at the seedling stage, but as they grow, effectiveness drops to about 40%. This weed control system is highly dependent on weather and soil conditions. In very wet springs, mechanical methods are difficult to apply. On heavily infested plots, it may even have the opposite effect, as damaged couch grass stolons are stimulated to grow and branch even more. Additionally, the mechanical system is the most costly and labor-intensive due to multiple passes. It is most often used in small farms, where potatoes are grown for self-sufficiency, and in organic systems. Before potato emergence, 3 to 6 treatments should be performed at 6–8 day intervals. After emergence, the number of cultivations should not exceed 2–3, and any delay increases the risk of crop damage, pathogen transmission through sap, and excessive soil drying (especially light soils).

Mechanical-chemical method

The most effective and widely used weeding system. It reduces the number of mechanical cultivations compared to the purely mechanical system. After planting, usually two or three hilling operations are carried out, followed shortly before emergence by herbicide treatment, after which no further cultivation is performed. During this growth phase, identifying weed species can be difficult; therefore, a treatment logbook, kept by each professional user of plant protection products, is essential to determine which weeds may pose a threat in a given field.

Chemical method

The most effective method is the use of herbicides, which are most efficient against this species at the seedling stage; the more advanced the growth, the lower the efficacy. Herbicides in potatoes are applied at two main times: before emergence and after emergence. Before using a herbicide, its label instructions must be followed for application timing and dosage. Some active substances have medium efficacy (average sensitivity of the weed species), and results may be unsatisfactory, especially when the weed is abundant or in an advanced growth stage.

On heavily infested plots, a non-selective herbicide containing glyphosate can be applied, known as the simplified system. Success depends on the presence of weeds, as glyphosate is absorbed only through leaves and cannot contact potato shoots (which would be destroyed!). Even potato sprouts just below the soil surface may be damaged. Correct timing according to weather conditions (temperature and rainfall) is crucial. Pre-emergence herbicides applied too late, when potato sprouts are just below the surface, may cause damage after heavy rain. Some pre-emergence products can still be applied in early growth stages, e.g., when potatoes are about 5 cm tall, such as prosulfocarb + metribuzin.

Active substances for pre-emergence control of small bugloss: chlornazon, linuron + chlornazon, metobromuron, metribuzin, metribuzin + chlornazon, pendimethalin. Post-emergence herbicides should be applied no later than the row closure stage to ensure full coverage and avoid accumulation of spray liquid on potato plants. Due to pre-harvest intervals, post-emergence herbicides cannot be used on early-harvest crops.

Active substances for post-emergence control of small bugloss: bentazon and metribuzin. Metribuzin applied post-emergence may cause phytotoxic symptoms on certain potato varieties.

Compiled by: Dr. Eng. Janusz Urbanowicz