Persian speedwell is an annual spring or winter weed from the dicotyledon class, which germinates mainly in spring, but also at the beginning of summer and autumn.

A characteristic feature of this species is the purple bloom on the hypocotyl and very long, hairy flower stalks.

It has a spindle-shaped taproot system. The stem is 10 to 40 cm high, round, branched, spreading, with two rows of protruding hairs. The stem can root. Cotyledons are round-ovate, 4 to 7 mm long, glabrous, green, rounded at the top, with a purple bloom underneath. True leaves are broadly ovate, with thick and deeply serrated margins; upper leaves are smaller, crenate-serrate, very rarely hairy. There is no inflorescence; flowers are single, growing from leaf axils on long, hairy stalks, bluish. The fruit is a reverse kidney-shaped capsule with a blunt tip, lightly net-veined, may be hairy or glabrous, containing 4 to 9 seeds. The seed is oval, warty, yellowish in color.

Occurrence and harmfulness

Persian speedwell occurs in cereal crops, mainly spring cereals, root crops, and gardens. It grows on clay, sandy-clay, humus-rich, and moist soils.

The harmfulness of Persian speedwell lies in its very rapid growth and the ability to flower and produce seeds throughout the growing season. It is a strong competitor for nutrients and is most abundant in wet years. Seeds can maintain high germination capacity for over 50 years. Optimal germination temperature is around 15–25°C, but it can germinate already at 2–5°C. It can germinate throughout the year, as the seeds do not undergo dormancy.

Control

Mechanical method

The long period from planting to potato emergence is a critical period (ideal conditions for weed development), which can be used for mechanical treatments. These are carried out using available farm machinery, e.g., ridgers, light harrows, inter-row cultivators, etc. Their main task is to create the most favorable conditions for rapid weed seedling emergence, followed by destruction through subsequent cultivation treatments. The highest effectiveness (even over 90%) can be achieved when weeds are at the seedling stage, but as weeds grow, effectiveness drops to around 40%. This system of weed elimination is highly dependent on weather and soil conditions. In years with very wet springs, the mechanical method is difficult to apply. On heavily infested plantations, it may have the opposite effect, as damaged couchgrass rhizomes are stimulated to even stronger growth and branching. Additionally, the mechanical system is the most costly and labor-intensive due to multiple passes. This method 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 damage, pathogen transmission with sap, and excessive soil drying (especially light soils).

Mechanical-chemical method

The most advantageous and widespread weed control system. It saves on mechanical cultivations, which are used much less than in the mechanical system. After planting, two or three ridgings are usually performed, followed shortly before emergence by herbicide application, after which no further cultivation treatments are conducted. At this stage of vegetation, identifying weed species can be difficult; therefore, a treatment log, kept and stored by every professional pesticide user, can serve as the basis for herbicide application. Based on it, one can determine which weed species may pose a threat on a given field.

Chemical method

The most effective method of control is the use of herbicides, which are most effective against this species when the weed is at the seedling stage; the more vigorous the growth, the lower the effectiveness. Herbicides in potatoes are applied in two main periods: before emergence and after emergence. After deciding to use a herbicide, one should read its label, which contains information on timing and dosages. Some active substances in herbicides have medium effectiveness (average sensitivity of the weed species), and the control effect may be unsatisfactory, especially when the species is highly abundant or in an advanced growth stage.

On heavily infested plantations, a non-selective herbicide containing glyphosate can be applied, which is the so-called simplified system. Its success depends on the presence of weeds on the plantation, as glyphosate is absorbed only through leaves and cannot affect potato sprouts (they would be destroyed!). Even potato sprouts just below the soil surface can be damaged (phot. A, B). Timing relative to weather conditions, especially temperature and rainfall, is crucial for its effectiveness. Pre-emergence herbicides applied too late, when potato sprouts are just under the soil surface, may damage the plants after heavy rain. Among pre-emergence herbicides, there are also registered products that can still be used in early growth stages when potato plants are about 5 cm tall, e.g., prosulfocarb + metribuzin.

Active substances controlling Persian speedwell for pre-emergence use: fluorochloridone, flufenacet + metribuzin, linuron + chlormazon, metobromuron, metribuzin, pendimethalin, prosulfocarb.

Post-emergence herbicides in potatoes should be applied no later than the row closure stage to ensure coverage of weeds and prevent the spray solution from staying on potato plants. Due to the length of the pre-harvest interval, post-emergence herbicides cannot be used in the earliest harvest!

Active substances controlling Persian speedwell for post-emergence use: bentazon and metribuzin. Metriibuzin applied post-emergence may cause phytotoxic reactions on some potato varieties.