Major Pests, Disease, and Weeds of Kiwi Plants and their Management

Kiwifruit is a resilient crop of high commercial value. In the previous articles of this cultivation guide, we focused on many important aspects of a successful cultivation plan to maximize production sustainably. Here, we will focus on plant protection and all the major crop "enemies" a kiwi grower should know, learn to recognize, and control in time to protect his/her crop and yield. Below, you will find information about the common kiwi pests and diseases, including their physiology, growth conditions, dispersal methods, and management strategies, the common physiological disorders that can be observed in kiwi plants, and finally, the most common weeds and their management.

The most common and Economically Important Kiwi Diseases

Pseudomonas syringae pv. actinidiae (PSA)

Pseudomonas syringae pv. actinidiae is the most important and destructive pathogen (bacteria) in kiwifruits, causing bacterial canker. It infects the plant through natural openings and wounds, causing symptoms such as leaf spots, cankers, and wilting. The bacterium produces several virulence factors, including extracellular polysaccharides and phytotoxins, which facilitate infection and disease progression. PSA thrives in cool, wet conditions, with high humidity and temperatures between 10-20°C (50-68°F) to be favorable to bacterial growth and dispersal. PSA can spread through rain splash, irrigation water, contaminated tools, and infected plant material. Farmers have difficulty controlling it and eradicating it once established in a plant (or even field) since it can survive on plant surfaces and in the soil, and no efficient control measures exist.

Management Practices

The first and most important preventive measure (to avoid infections and dispersal) is sterilizing tools and equipment used in the field (e.g., for pruning). In areas where PSA is a common problem, farmers are advised to plant PSA-resistant kiwifruit cultivars (consult your agronomist or plant nurseries in your region). Regular inspections and promptly removing infected plants to prevent the spread are also important. Immediate action is needed upon detection of any PSA symptoms. To decrease the risk of infection, pruning and harvesting should be performed in dry weather (at least two days before and two days after). It is important to create a well-aerated canopy to decrease humidity levels. Finally, the infected plant material should be removed from the field once spotted. Application of copper-based bactericides and other registered products might be necessary in some cases. However, you need to consult your local licensed agronomists before making an application and always read and follow the guidelines on the product label.

Botrytis cinerea (Gray Mold)

Botrytis cinerea is a fungal pathogen causing gray mold in kiwifruit. The fungus infects flowers, leaves, and fruit, leading to rotting and significant crop losses. It produces spores (conidia) and sclerotia, which can survive in plant residues and soil for long periods (years). Cool-weather (15-25°C (59-77°F)) and high humidity are optimal for fungal growth and spore germination. The dispersal of the pathogen (as conidia) can happen by wind, rain, and irrigation water. Infection often occurs through wounds or natural openings in the plant tissue, particularly under wet conditions.

Management Practices

Management measures should be taken if gray mold is observed on 1-2% of the plants, especially during flowering and early fruiting stages. The farmer should remove and destroy (usually by burning) the infected plant parts to reduce inoculum sources in the field. Proper pruning may help by improving air circulation within the kiwifruit plant canopy (and tunnels), and overhead irrigation must be avoided (prefer drip irrigation). The application of fungicides, particularly during flowering and fruit set, might be necessary as a preventive and control measure. Growers are advised to stay informed and follow the recommendation of local extension centers reports.

Phytophthora spp. (Root Rot)

Phytophthora can cause root rot in kiwifruit, and the infected plants exhibit symptoms such as wilting, stunted growth, and root necrosis. The pathogen thrives in wet, waterlogged soils with poor drainage, especially in mild temperatures (15-25°C (59-77°F)). Zoospores are dispersed through water flow in the soil. Infection occurs primarily through the roots, leading to systemic disease in the plant.

Management Practices

Ensuring good soil drainage in the field and avoiding over-irrigation and good air circulation on the plantation are essential. In fields with a known history of the disease, the farmer should choose resistant rootstocks (grafted plants). Action is required if symptoms such as wilting or root necrosis are observed in 1-2% of the plants, as Phytophthora can spread rapidly under optimum conditions. Applications with fungicides and phosphonates in the soil should be applied after consulting your agronomists or extension center.

Sclerotinia sclerotiorum (White Mold - Flower Blight)

Sclerotinia sclerotiorum is a fungus causing white mold in kiwifruit. It can affect flowers, shoots, and leaves, leading to important yield losses in kiwi production. Common symptoms that may be observed are:

Water-soaked lesions.
Flower blight.
Fruit scarring.
Premature fruit drop.
The appearance of white mycelial growth in the infected plant tissues.

Sclerotia (resilient survival structures) produce spores that infect plant tissues. The pathogen can spread through contact with infected plant material (e.g., with tools and machinery) and soil. High humidity and temperatures between 15-20°C (59-68°F) favor disease development.

Management Practices

Good sanitation is the basic and most important preventive measure. All infected plants, plant parts, and residues should be removed from the field and destroyed. Good air circulation to decrease humidity in the plant canopy and a suitable crop rotation system can also help prevent or manage the problem. Control measures should be initiated if white mold is detected on 1-2% of the plants, particularly during the flowering period of kiwi and when the environmental conditions are optimum for the pathogen. For organic producers, the use of biocontrol agents such as Coniothyrium minitans, which parasitize the fungus, can be beneficial. Many farmers choose to perform timely application of fungicides. You must always consult a local licensed agronomist before applying any chemical.

Kiwi Major Pests and Their Management

**Armored Scale Insects (*Hemiberlesia rapax***)

Armored scales, commonly known as greedy scales, are small, sessile insects that attach to the kiwi plant leaves, cordons, canes, and fruits, feeding on plant sap. The pest has a hard protective covering that shields it from predators and pesticides.

Farmers should encounter them in their fields in different forms/developmental stages: eggs, crawlers (mobile nymphs), and adults. Armored scales thrive in warm, dry climates, and high temperatures and low humidity levels favor their development and population growth. Crawlers, the only mobile stage, disperse by crawling to new feeding sites or being carried by wind, animals, or human activities. Infestations can spread rapidly, causing significant damage by weakening the plant, reducing fruit size, and potentially transmitting plant pathogens.

Management Practices

Regular inspections for early detection of infestations are needed to decrease the losses and keep the pest population under control. Treatment is recommended when scales are observed on more than 10% of the plant's leaves or fruits or when there is a noticeable increase in scale population over time.

Biological and Cultural Measures: The introduction of natural predators such as lady beetles and parasitic wasps can help keep the population under control. That is more of a preventive practice. Pruning infested branches and maintaining plant health can help reduce the population and plant susceptibility.
Chemical Control: Horticultural oils and systemic insecticides might be necessary when we have reached the action/economical threshold. The application should be timed to target the crawler stage for maximum effectiveness and always performed with certified and suitable pesticides after consulting your local licensed agronomist.

**Brown marmorated stink bug (BMSB), (*Halyomorpha halys***)

This stink bug is an invasive pest native to East Asia that is considered an important emerging kiwifruit pest, especially in fields of Greece, Italy, and the USA. While the insect is not new to the farmers in these regions, in the past few years, its population has increased and can cause measurable damage to the fruits if left uncontrolled. The problem can be more severe in high-density kiwi plantations. Based on research findings and farmers' experience, it seems that the insect is favored by high humidity levels. The adults can travel more than 5 km per day. Farmers often choose to apply 1-2 sprays with chemicals to control the BMSB and limit any possible damage (even when the populations are still not at threatening levels). While an efficient and clear control strategy for the pest still has not been found, scientists in Europe are experimenting with the egg parasitoid Anastatus bifasciatus Geoffroy, which seems to be a promising candidate for biological control of the BMSB.

**Leafroller Caterpillars (*Ctenopseustis obliquana***)

Leafroller caterpillars are larvae of moths that feed on kiwifruit leaves, buds, and fruit. They create shelters by rolling leaves together and securing them with silk. The caterpillars undergo complete metamorphosis, from egg to larva to pupa to adult moth. Pests prefer moderate to warm temperatures and high humidity, and their activity peaks in spring and summer when new vegetative growth is abundant. Adult moths lay eggs on the leaves, and the emerging larvae feed on the foliage and fruit.

Management Practices

Regular scouting of the field to find rolled leaves, egg masses, and larvae should be performed, especially during spring and summer.

Biological and Cultural Management: The farmer should take measures to boost and protect the population of beneficial insects (natural enemies of pests such as parasitoid wasps and predatory insects) or introduce them to the field. Removal of infested plant parts and maintaining orchard hygiene can also help.
Chemical Control: The farmer should apply chemical control only when there is no other option and when the infestation/damage from the pest has reached the action threshold (5-10% of the shoots or fruit clusters show signs of infestation). Targeted use of insecticides, particularly during the larval stage, is recommended. Before any action, you must consult a licensed agronomist.

**Greenhouse Thrips (*Heliothrips haemorrhoidalis***)

Greenhouse thrips are small, black insects with fringed wings that feed on the undersides of kiwifruit leaves, causing silvering and scarring, leading to measurable stress on the plant and yield losses if left uncontrolled. The insects are favored and thrive in warm, humid environments.

Management Practices

To successfully manage thrips, the farmer should take preventive measures and use an integrated approach (e.g., introducing predatory mites and insects). Chemical control (insecticidal soaps and horticultural oils) should be limited since the pest can develop resistance to the pesticides quite fast.

Physiological Disorders in Kiwi Plants

Like other fruit crops, Kiwifruit plants can suffer from some physiological disorders that affect their growth, fruit quality, and overall health. These disorders are often caused by environmental stresses, nutrient imbalances, or cultural practices rather than infectious agents like pests and pathogens.

Chlorosis

In kiwi plants, chlorosis typically occurs due to iron deficiency (a very common problem in kiwifruit plantations), though it can also result from deficiencies in other micronutrients such as manganese or zinc. Alkaline soil conditions (high pH), which hinder nutrient uptake, are often the underlying cause. Common symptoms include yellowing between the veins of younger leaves while the veins remain green. The most common way to address this problem is soil pH adjustment (lowering) by adding sulfur or using acidifying fertilizers. For immediate results, farmers can apply foliar sprays with the nutrients needed. A soil and plant tissue analysis is necessary to diagnose the problem.

Sunscald - Sunburn

Sunburn is usually expressed as bleached or necrotic patches on the sun-exposed sides of the fruit and leaves, leading to reduced marketability and shelf life. Leaves may also show signs of browning or scorching. Of course, the problem is more frequent and severe in warm climates during the warm summer months. To protect their crops and production, kiwifruit growers should apply proper pruning to develop a robust canopy that can provide natural shading for fruit and leaves. In some cases, installing nets above the plants' canopy can offer beneficial shade.

Fruit Deformities - Butterfly-like Kiwifruits

Fruit deformities, including malformed or undersized fruits, can result from poor pollination, nutrient deficiencies, or environmental stresses. These deformities affect the commercial value of the kiwi fruit. One of the most commonly encountered in kiwifruit plantations is the butterfly effect (fruits that look like "Siamese twins," resembling the wings of a butterfly). These fruits are usually removed from the plants as soon as they are observed since they have very low or no economic value. Ensuring adequate pollination by maintaining a proper ratio of male to female plants and using bee attractants can improve fruit set and quality.

Common Weeds in Kiwi Fields and Their Management

Kiwifruit growers manage the weeds in their fields to reduce competition with the crop for nutrients and water. This process is especially important in newly planted fields. Below, we list some of the most common and important weed species that can be found in kiwifruit fields and some management practices.

Annual Grasses

They are commonly seen in kiwifruit fields (especially in spring and summer) and can be managed relatively easily.

Barnyardgrass (Echinochloa crus-galli) and Crabgrass (Digitaria spp.) Both species are annual grasses that thrive in disturbed soils and can quickly dominate if not managed (especially the barnyardgrass). These weeds can compete with kiwi plants for essential resources and can harbor destructive pests and diseases, causing problems for the crop.
Chickweed (Stellaria media) and Shepherd's Purse (Capsella bursa-pastoris): Both are winter annuals that germinate in the fall, overwinter as a small plant, and complete their life cycle in the spring. They emerge early and quickly cover the ground, competing with kiwi plants during critical early growth stages.

Perennial Broadleaves

Dandelion (Taraxacum officinale) and Plantain (Plantago spp.): Both weeds have deep taproot, making it difficult to eradicate once established in a field. They can spread easily if not managed. The weeds compete vigorously with kiwi plants, particularly for water and nutrients, and can be hosts for important crop pests.
Field Bindweed (Convolvulus arvensis): Bindweed is a perennial creeping weed that can smother young kiwi plants. It is highly competitive and often requires persistent control measures.
Bermuda Grass (Cynodon dactylon): Bermuda grass is another creeping perennial grass that spreads via stolons and rhizomes. It can compete for nutrients and water, making it difficult for kiwi plants to establish and grow.

Weed Management Practices for a Kiwi Field

Farmers are advised to adopt an Integrated Weed management approach to achieve the best, longest-lasting results with limited negative environmental effects. At the same time, this approach protects the health of the plants and the production and quality of the fruits.

Cultural Practices
- Mulching: Applying organic or synthetic mulches can suppress weed growth by blocking light and preventing weed seed germination. Mulches also help conserve soil moisture and improve soil structure. The farmer can cut the weeds during the summer months and leave them on the field floor.
- Cover Crops: Planting cover crops during the off-season can outcompete weeds, decrease their population, improve soil health, and reduce erosion. Legumes are a common good choice that can also fix nitrogen, enhancing soil fertility.
- Precise Irrigation: Efficient irrigation practices, such as drip irrigation, target water to kiwi plants and reduce water availability to weeds.
Mechanical Control
- Tillage: Tillage can help manage annual weeds by uprooting them. However, it has numerous negative effects and should be applied with caution. Apart from increasing the risk of soil erosion, it might also favor some weeds (e.g., the ones reproducing with stolons), increasing the problem. Farmers should record the weeds in their fields before deciding on the management strategy. Additionally, soil disturbance during summer is best to be avoided (not reduce soil moisture).
- Hand Weeding: Manual removal of weeds is effective, especially for small infestations or in organic orchards, but is rarely preferred in large commercial kiwifruit plantations.
- Mowing: Regular mowing of the orchard floor can keep weed growth in check and prevent the establishment of perennial weeds. At the same time, introducing animals into the crop could have other benefits, but it should be done with caution to avoid any damage to the lower branches of the plants.
Chemical Control

The use of pre-emergent and post-emergent herbicides can be effective in controlling weeds in Kiwi fields. Herbicides must be used in combination with the above-mentioned practices to avoid the development of herbicide-resistant weeds. The farmer can use selective or nonselective herbicides depending on their needs. Be careful not to wet the crop canopy, which can cause plant toxicities. You must always consult your local licensed agronomist before applying any chemical. Regularly monitoring and assessing weed populations helps make informed decisions and adjust management practices accordingly. By integrating cultural, mechanical, and chemical control methods, farmers can effectively manage weeds, ensuring good crop health and fruit production.

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Major Pests, Disease, and Weeds of Kiwi Plants and their Management