Blog 9 – Plant Disease & Insects

Most important insects and diseases for pecans

The main occurring insect pests are listed in table 1.

Table 1 The main insect pests in pecan cultivation (Ellis, Bertrand, Hudson, & Georgia, 2009).

Blackmargined aphid	Spittlebugs	Pecan leaf casebearer
Yellow pecan aphid	Nut curculio	Pecan cigar casebearer
Black pecan aphid	Hickory shoot curculio	Pecan nut casebearer
Pecan leaf scorch mite	Hickory shuck worm	Walnut caterpillar
Pecan phylloxeras	Pecan weevil	Twig girdler
Pecan serpentine leafminer	Southern green stink bug	May beetles
Upper surface blotch leafminer	Leaffooted bug	Sawflies
Fall webworm	Pecan bud moth	Pecan catocalas

In most cases of disease, it was carried by a host, such as insects. Therefore, insect management is not only to the damage they may do personally, but also for the potential pests they carry.

Table 2 The main diseases in pecan production, adapted from (Arena, Kluepfel, Blake, & Reilly, n.d.), (Texas A&M Agrilife Extension, n.d.).

Disease	Type of disease
Scab	Fungal Pathogen
Downy Spot	Fungal Pathogen
Brown Leaf Spot	Fungal Pathogen
Vein Spot	Fungal Pathogen
Leaf Blotch	Fungal Pathogen
Powdery Mildew	Fungal Pathogen
Pecan Bacterial Leaf Scorch (BLS)	Fungal Pathogen
Articularia Leaf Mold	Fungal Pathogen
Pink Mold	Fungal Pathogen
Cotton Root Rot	Fungal Pathogen
Shuck and Kernel Rot	Fungal Pathogen
Stem End Blight	Fungal Pathogen
Kernel discoloration	Fungal Pathogen
Fungal Twig Dieback	Fungal Pathogen
Crown Gall	Bacterial Pathogen
Shuck Dieback	Plant disorder
Bunch Disease	Plant disorder
Parasitic and epiphytic plants	Plant disorder
Root Knot Nematode	Nematode

Insects can be hosts for both fungal and bacterial pathogens. (Agrios). This is why it is important to mention next to the disease to gain understanding of its characteristics and origin of infection. As we can determine from the list in table 2, the most occurring diseases are fungi. That makes moisture a problem, for it is often the cause for fungi growth.

The most common pecan disease is scab. The fungi associated with this disease is Cladosporium caryigenum. They are in hibernation in winter, but become active in spring when a result small round spots will arrive on leaves, stems and husks of the nuts. Younger trees and new grown leaves and stems are most vulnerable for scab. (Barth, n.d.).

Squirrels, crows and blue jays could also cause nut losses. In some regions deer, raccoon and rats also cause the same type of problems. (Ellis, Bertrand, Hudson, & Georgia, 2009).

How would an integrated pest management (IPM) strategy for your crop look like?

Scab control is done by making sure that there is a dry air flow around the tree and fallen leaves are picked up relatively soon after dropping to the ground. Chemical control is done by spraying fungicides, such as thiophonate-methyl. Fungicides, however, could disrupt the ecosystem around the trees and is less sustainable than the former mentioned method. The last option is to plant scab-resistant cultivars. Examples are the widely used Elliot, though it takes a long time before when one can harvest the crop. For Northern growers the Kanzi is recommended. Other examples of cultivars are Amling, Excel and Lakota. (Barth, n.d.). Since most of the other diseases are also fungicides this method will also be applicable for controlling them, though the needed type of fungicide could be different. (Ellis, Bertrand, Hudson, & Georgia, 2009).

Weed control, by e.g. growing grass or clover (See blog 8 – Weeds) helps to get rid of unwanted insects. As mentioned earlier the insects can be harmful themselves but could also potentially carry fungal or bacterial pathogens. This is why weed control is of big importance in pecan cultivation. Chemical control of the insects can be reached by using herbicides. Just as with the fungicides, however, they can be harmful for the ecosystem.

Methods to prevent damage of squirrels, crows and blue jays can achieved by fencing, placing nets and rapid harvest. (Ellis, Bertrand, Hudson, & Georgia, 2009).

Bibliography

Agrios, G. (n.d.). TRANSMISSION OF PLANT DISEASES BY INSECTS. Gainesville, Florida, USA: University of Florida. Retrieved from http://entomology.ifas.ufl.edu/capinera/eny5236/pest1/content/03/3_plant_diseases.PDF

Arena, M., Kluepfel, M., Blake, J., & Reilly, C. (n.d.). Pecan Diseases. Retrieved from Clemson University: https://www.clemson.edu/extension/hgic/pests/plant_pests/veg_fruit/hgic2211.html

Barth, B. (n.d.). Pecan Scab Control. Retrieved from SF Gate: http://homeguides.sfgate.com/pecan-scab-control-81755.html

Ellis, H., Bertrand, P., Hudson, R., & Georgia, U. o. (2009). Pecan pest and disease management. Retrieved from Bugwood wiki: https://wiki.bugwood.org/Pecan_pest_and_disease_management#Insect_Pests

Texas A&M Agrilife Extension. (n.d.). Texas Plant Disease Handbook. Retrieved from Texas A&M Agrilife Extension: https://plantdiseasehandbook.tamu.edu/food-crops/nut-crops/pecan/