Keeping herbs pest-free

MANILA, Philippines – Long before the dawn of state-of-the-art medical facilities and doctor-prescribed pills were herbs and spices. They are nature’s gift to communities surrounded by lush greenery instead of the drowning concrete gray in highly urbanized areas. Herbs and spices used to be readily available in our backyard, freely growing in our garden beds until someone in the family gets sick and our mothers would quickly prune a few leaves, have them boiled and ready to soothe our pains.

Herbs and spices also enhance the taste of food, deodorize living places, adding a pleasing scent around homes and other spaces. Additionally, they have also been proven to be essential raw materials for local enterprises in making soap, massage creams, body scrubs, ointments, and tea. Farmers who practice organic agriculture would extract and ferment the juice from harvested herbs so they may use it as an alternative to chemical sprays.

Recognizing the significant roles herbs and spices play in Philippine agriculture, the University of Southern Mindanao in partnership with the Bureau of Agricultural Research conducted a research on the dentity, incidence, and severity of insect pests and diseases affecting selected spices.

Leaf blight was seen to be common in samples of pandan and basil. Symptoms of this fungus-induced disease are brown blotches appearing on the leaves which eventually increase in size causing the infected leaves to wither. The cause of leaf blight in pandan is a fungus called Fusarium moniliforme which usually targets plants rich in carbohydrates and oil. This fungus is also the cause of leaf spots in turmeric. 

Also noted were leaf and stem algal spots caused by an organism called Cephaleuros virescens. This pest usually targets leaves with a shiny leather surface and can also easily thrive in moist areas. If an herb is infected with this disease, its leaves would exhibit grayish, green, brown, or orange cushion-like blotches on the leaf surface. This disease was highly observed in black pepper, langkawas, and laurel.

Stem blight in tarragon, on the other hand, is caused by Sclerotium rolfsii, a fast-spreading fungal pathogen that develops on plant surfaces that come in contact with soil. Symptoms of the presence of the disease are silky-white filaments covering specific plant parts that touch the ground.

 Fruit rot in achuete and annato was also observed during the study. Signs of this disease are emerging white spores surrounding fruits that eventually turn into a darker shade. This can affect the soft tissues of harvested fruits causing them to rot and leak watery substances.

 Some herbs were also found infected with various virus diseases which are suspected to be carried by alternate hosts.  These virus diseases include chlorotic streaks in lemongrass and mosaic virus in oregano. Symptoms of mosaic virus include yellow stripes or spots on plant foliage as well as wrinkled and curled leaves.

Viruses would have most likely been spread by vectors or carriers such as colonies of ants and aphids.

As for insect pests, leaf rollers, green peach aphids, bagworms, weevils, mealybugs, and scale insects made up the majority of pests observed among the planted herbs and spices.

The research team explored the dynamics of the pests and diseases among herbs and spices and the cultural practices used to propagate them as well as the effects of different weather occurrences throughout the research period. 

The study concluded that planting herbs that are appropriately distanced from each other, applying organic fertilizer, and frequent weeding are cultural practices that are critical to controlling the spread of pests and diseases. 

For example, increasing the planting distance of basil from 10cm x 30cm to 30cm x 30cm decreased insect counts by almost 20 percent. The same is true with oregano. 

The organic fertilizers used during the research included chicken dung, Grassroots Integral Development Initiative (GIDI) Natural Organic Fertilizer, vermicompost, and Mycovam. 

When GIDI was used on basil, not only did the cultural practice lessen the incidence of pest, but also increased the herbal plant’s biomass. 

The effect of weather occurrences resulted to different trends between insect population and disease severity. For data on the population of insects, there tends to be a decrease when humidity is high and an increase in insect population during hotter days.

As for diseases, such as powdery or downy mildews, stem blight, wilts, leaf spot, and leaf blight, spices tend to exhibit more severe infections under higher temperatures, increased relative humidity, and more intense rainfall.

The research team noted that pest management greatly depends on how you maintain herbs and spices garden in tip-top shape. 

A good cultural practice is making sure that the soil in which the herbs grow is clear of dead, fallen leaves as this may be the source and breeding ground for fungi and pests. 

Infected plants must also be gotten rid of to keep the pests and diseases from being transferred, not only to the plants around it but also to the next batch of seedlings. - Ephraim John J. Gestupa