Weedkiller damage

Weedkillers (herbicides) are products designed to kill plants. They affect many types of plants, not only the ones they are intended for. 

Non-chemical weed control

Weeds in lawns

Weeds on hard surfaces

Contact weedkillers

Symptoms:

• Soft stems and leaves sprayed or splashed with contact weedkillers usually develop a scorched appearance or brown spots.

Contact weedkillers, such as those containing acetic acid or pelargonic acid, are non-selective and work by killing the sections of plant where the spray droplets land.

Hormonal weedkillers

Symptoms:

• Narrowed or cup-shaped leaves with parallel veins
• Twisted or distorted leaf stalks
• Adventitious
  Adventitious refers to a root or shoot that forms in an unusual location, such as from a stem or leaf. Adventitious roots often help a plant anchor itself, as in the case of those produced from ivy and pothos stems. Both adventitious roots and shoots are produced by leaf cuttings to create new plants, and by many types of orchid when they produce keikis (plantlets) from flowering stems. roots on some plants, including root crops
• Swollen stems, galls or warts on brassicas and other plants
• Plum-shaped and distorted tomatoes with hollow centres

Hormone

Chemical substances that regulate plant growth and development. There are several types of plant hormones, including auxins, cytokinins, gibberellins, abscisic acid and ethylene. These hormones play important roles in processes such as cell division, elongation and differentiation, as well as in responses to environmental stimuli such as light and gravity. or growth-regulating weedkillers, such as those containing clopyralid and triclopyr, are selective. They damage broad-leaved plants while leaving grasses unharmed. Roses, tomatoes, potatoes and vines are particularly sensitive to hormonal weedkillers.

Hormonal weedkillers are foliar-acting and systemic (translocated), moving down into the weeds' roots when applied to the leaves. Residues can persist in treated plant material for months.

Systemic (translocated) weedkillers

Symptoms:

• Leaf yellowing or browning, the collapse of soft stems, stunted growth and deformed leaves. If particularly sensitive plants, such as roses and raspberries, are sprayed in late summer, deformed growth may not appear until the following season.
• Clusters of short, pale shoots that resemble mini witches’ brooms are produced by some plants, including roses.

Systemic weedkillers containing glyphosate are non-selective. Glyphosate kills broad-leaved plants and grasses. When applied to leaves, glyphosate moves down into the root system and can kill even deep-rooted plants.

Residual weedkillers

Symptoms:

• Leaf yellowing or dieback. It may take several weeks before damage becomes visible.

Residual weedkillers, such as diflufenican, are designed to remain in the soil for weeks and sometimes months. Damage can occur if roots growing below treated surfaces take up residual weedkillers.

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Shutterstock

• Using products in breezy conditions increases the chance that spray will drift onto nearby plants. Smaller droplets are more easily carried sideways, so fine sprays are more likely to move off course. 
• Using a sprayer or watering can that contained weedkiller and hasn’t been rinsed and cleaned sufficiently.
• Residual weedkiller can move down through the soil and be taken up by plant roots. This can happen if too much weedkiller is sprayed on an area, or on light sandy soils where it can easily move down into the soil.  
• Mulching
  Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings. with grass clippings (or compost
  Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. that contains them) from lawns treated with selective hormone
  Chemical substances that regulate plant growth and development. There are several types of plant hormones, including auxins, cytokinins, gibberellins, abscisic acid and ethylene. These hormones play important roles in processes such as cell division, elongation and differentiation, as well as in responses to environmental stimuli such as light and gravity. -type weedkillers, such as clopyralid.
• Using bought-in composted green waste
  Plant-based waste that is suitable for composting, such as dead leaves, clippings from pruning or grass mowing and discarded annuals. Many local councils have green waste recycling schemes if home composting isn't an option. or manure contaminated with persistent hormonal weedkillers, such as aminopyralid.
• Misapplying or using the wrong type of weedkiller or other chemical, such as household bleach, vinegar, washing-up liquid and cleaners (these can cause serious plant damage and environmental harm).
• Vandalism: this is rare but there have been cases of malicious and deliberate damage to plants using weedkillers.

There are several ways to deal with weedkiller damage:

• Prune out any abnormal, yellow, brown or dead growth.  It may be some time before affected plants start to produce normal shoots again.
• Speed up recovery of damaged plants by ensuring they are well looked after. Water during dry spells, mulch around permanent plantings, and feed if growth is particularly slow. Plants showing symptoms of hormone
  Chemical substances that regulate plant growth and development. There are several types of plant hormones, including auxins, cytokinins, gibberellins, abscisic acid and ethylene. These hormones play important roles in processes such as cell division, elongation and differentiation, as well as in responses to environmental stimuli such as light and gravity. weedkiller contamination early in the growing season may grow out of the problem as the chemical residues break down. Many plants recover with time, especially when growing conditions are improved.
• Only replant after sufficient time has elapsed for weedkiller residues to break down (check weedkiller label for details). Not all weedkiller damage results in plant death. Trees, shrubs and herbaceous perennials
  Perennials are plants that live for multiple years. They come in all shapes and sizes and fill our gardens with colourful flowers and ornamental foliage. Many are hardy and can survive outdoors all year round, while less hardy types need protection over winter. The term herbaceous perennial is used to describe long-lived plants without a permanent woody structure (they die back to ground level each autumn), distinguishing them from trees, shrubs and sub-shrubs. accidentally damaged by a contact weedkiller usually recover; those treated with glyphosate may survive but some root damage is likely.
• Report incidents of damage caused by weedkiller contamination in compost
  Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. or manure you have bought. You can report this to the Health and Safety Executive and/or Corteva (the manufacturers of clopyralid and aminopyralid, two hormone-type weedkillers that take a long time to break down after binding to grass). You should also contact the manufacturer of the compost/manure, giving details of where and when it was bought.
• Carry out a germination
  Germination is the process by which a seed develops into a new plant. It starts with the seed coat absorbing water, expanding and splitting, which allows oxygen and water into the seed so its food reserves can be broken down and used by the embryo for growth. The first root (called the radicle) pushes into the soil to anchor the new plant in place and start absorbing water and nutrients. The first shoot (called the plumule) then grows upwards, out of the soil, towards the light. test if you suspect growing media or organic matter you have bought contains hormone weedkiller. See the section below for a step-by-step guide to doing a germination test.
• Record damage if vandalism is suspected; photographs of affected plants can be useful. These may be needed for evidence if the matter is taken further. Weedkiller residues are difficult to test for in plant material (the RHS does not have the facilities needed to offer this service) but a report from a horticultural consultant may be worth considering.  

If you suspect your own garden compost

Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. , or commercially produced compost or organic matter is contaminated by weedkiller, you can do a simple test for weedkiller residue:

STEP 1: Fill two clean pots with the suspect growing media (fresh, not used) and label. Pots don’t need to be any larger than 1 litre in size.

STEP 2: Fill two more clean pots with garden soil or another brand of growing media as a control and label.

STEP 3: Into each pot sow four broad bean seeds. Broad beans are sensitive to weedkiller and quick to germinate, so are a good choice. Water well with tap water.

STEP 4: Place the pots in a greenhouse or on a warm windowsill. Keep the compost slightly moist, ensuring the drainage water from the pots containing the suspect growing media cannot contaminate the control ones.

STEP 5: If, after three weeks, the seeds in the suspect growing media fail to emerge, or the seedlings

A seedling is a young plant grown from seed. are distorted, slow-growing, or exhibit fern-like growth, while control plants are normal, there are strong grounds to believe weedkiller residues are present.

If the test is positive, report your findings to the compost manufacturer and the Health and Safety Executive. Compost suspected of containing hormone

Chemical substances that regulate plant growth and development. There are several types of plant hormones, including auxins, cytokinins, gibberellins, abscisic acid and ethylene. These hormones play important roles in processes such as cell division, elongation and differentiation, as well as in responses to environmental stimuli such as light and gravity. weedkiller residues can be used as a topdressing for lawns.

Non‑chemical weed control removes the risk of spray drift, residues and accidental damage. Many gardeners find that mulching

Mulch is a layer of material, at least 5cm (2in) thick, applied to the soil surface in late autumn to late winter (Nov-Feb). It is used to provide frost protection, improve plant growth by adding nutrients or increasing organic matter content, reducing water loss from the soil, for decorative purposes and suppressing weeds. Examples include well-rotted garden compost and manure, chipped bark, gravel, grit and slate chippings. , hoeing

Hoes are multi-purpose tools for weeding (especially between rows of veg), loosening the soil surface, making seed drills, earthing up plants, and more. There are various types with different shaped blades. Hoeing to remove weeds is best done on a warm, dry day, so you slice easily through weed stems just below the surface. , hand‑weeding and ground cover planting are effective methods of weed control. The RHS does not support the use of weedkillers.

If weedkillers are used, the risk of accidental damage can be reduced by:

• Following the product label
  This is a legal requirement. Information and instructions on the label should be read before buying and using any weedkiller product.
• Checking the weather conditions
  Avoid windy, hot or very sunny conditions, and avoid spraying during drought.
• Using separate equipment for herbicides
  Sprayers or watering cans used for weedkillers should be kept separate from those used for other garden products.
• Cleaning equipment thoroughly after use
  Sprayers or watering cans should be triple‑rinsed after use, and the rinsings should only be applied to areas listed on the label. Ready‑to‑use products avoid this step.
• Following instructions on disposal of lawn clippings
  Selective lawn weedkiller labels state when clippings can be collected and how long they need to be composted before residues break down. If you use a lawn‑care company, ask whether weedkillers have been applied.
• Keeping treated clippings out of green‑waste bins
  Clopyralid and similar persistent weedkillers can survive the green‑waste composting
  Composting is the process by which plant material is heaped together to rot (decompose) to produce compost. Garden or kitchen waste can be broken down over time in a compost bin or heap to produce crumbly organic matter that can be used as a mulch, soil conditioner and a constituent of potting compost. process and contaminate compost
  Can refer to either home-made garden compost or seed/potting compost: • Garden compost is a soil improver made from decomposed plant waste, usually in a compost bin or heap. It is added to soil to improve its fertility, structure and water-holding capacity. Seed or potting composts are used for growing seedlings or plants in containers - a wide range of commercially produced peat-free composts are available, made from a mix of various ingredients, such as loam, composted bark, coir and sand, although you can mix your own. sold to gardeners.
• Avoiding tracking weedkiller around the garden
  Weedkiller can be transferred on footwear or tools.
• Taking extra care around plants that sucker
  Suckers are growths that appear from the root systems of many trees and shrubs such as lilac, cherries, Robinia. On grafted plants such as roses, suckers can grow from below the graft union, on the rootstock material. Suckers are usually removed by gently pulling off when young. or regenerate from roots
  Spraying suckers or connected shoots with a systemic weedkiller can damage the parent plant.
• Choosing compost carefully
  Select peat-free growing media that clearly states it contains no composted green waste
  Plant-based waste that is suitable for composting, such as dead leaves, clippings from pruning or grass mowing and discarded annuals. Many local councils have green waste recycling schemes if home composting isn't an option. . Alternatively, make your own mixes.
• Shielding nearby plants if spraying
  A hood on a sprayer can help reduce drift if a herbicide must be applied.