Michelle M. Cram

The association of a Longidorus species with stunting and root damage of loblolly pine (Pinus taeda L.) seedlings

A Longidorus species was consistently associated with patches of stunted and chlorotic loblolly pine seedlings at a forest-tree nursery in Georgia. Seedlings from affected areas had poorly developed root systems that lacked lateral and feeder roots. Longidorus population densities in composite soil samples from the margins of patches ranged from 9 to 67 nematodes per 100 cm3 of soil. In a growth chamber experiment, seedling root dry weight decreased with respect to the initial Longidorus dose as well as the final Longidorus populations in containers. The dry root weight of seedlings were 0.117, 0.090, 0.066, and 0.065 g in containers initially infested with 0, 50, 100, and 200 Longidorus, respectively. Lateral and fine roots were lacking on seedlings at the highest doses. Populations of Longidorus increased in all containers during the experiment. Damage to loblolly pine seedlings caused by Longidorus is a previously undescribed problem in southern pine nurseries. Proper diagnosis of the problem by nematode testing laboratories may require the use of extraction techniques specific for larger nematodes such as Longidorus.

Matsucoccus macrocicatrices (Hemiptera: Matsucoccidae): first report, distribution, and association with symptomatic eastern white pine in the Southeastern United States.

ABSTRACT We provide the first report of Matsucoccus macrocicatrices Richards (Hemiptera: Mat-sucoccidae) feeding and reproducing on eastern white pine, Pinus strobus L., in the southeastern United States. Until now, M. macrocicatrices had been reported only from the Canadian Atlantic Maritimes, New Hampshire, and Massachusetts. Entomological holdings of 27 major museums in eastern North America have no historical records for M. macrocicatrices from the southeastern region. However, our field surveys and molecular analyses (DNA barcoding) have resulted in the collection and positive identification of M. macrocicatrices in Georgia, North Carolina, South Carolina, Tennessee, Virginia, and West Virginia. In addition to the new geographic range, M. macrocicatrices is also being associated with dieback and mortality of all diameter classes of P. strobus leading to concern about a potential shift from its historically nonpestiferous presence on the host tree. On P. strobus, M. macrocicatrices was found embedded in cankers or present on top of the bark with necrotic tissue under their feeding area, indicating that they may be creating wounds for opportunistic pathogenic fungi to infest. Further, we found M. macrocicatrices living outside of the epiphytic mats of its symbiotic fungus, Septobasidium pinicola Snell. This study shows that M. macrocicatrices is now widespread in the southeastern United States, with implications for the future survival and regeneration of P. strobus in eastern North America.

Suitability of southern pines, other selected crops, and nutsedge to a Longidorus sp. associated with stunting of loblolly pine seedlings

An undescribed needle nematode (Longidorus sp.) has been associated with severely stunted loblolly pine seedlings at a south Georgia nursery. Containers with selected crop and weed species were infested with 100 or 200 adults and juveniles of the Longidorus individuals to evaluate host suitability. Nematode populations increased in containers with slash, loblolly, and longleaf pine seedlings. The Longidorus sp. significantly reduced the dry root weights of slash (P = 0.008) and loblolly (P = 0.047) but not longleaf (P = 0.095) pine compared with controls. Populations of Longidorus decreased on nutsedge and small grains, including wheat, rye, oat, sorghum, and millet; and, in most experiments, populations decreased to levels found in fallow containers. Populations decreased on tomato and cabbage but increased slightly on red oak. The periodic removal of fields from pine production to grow cover crops consisting of small grains or to maintain fallow fields may be an important practice for management of this Longidorus sp.

The effect of fallow on Longidorus americanus, a nematode associated with stunting of loblolly pine seedlings in Georgia, USA

Stunting of loblolly pine (Pinus taeda L.) seedlings, caused by Longidorus americanus, has been a problem at a Georgia (USA) nursery. Field and growth chamber studies were conducted to determine the survivability of the nematode in fallow nursery soil. The population density of L. americanus decreased rapidly in the upper 15 cm of soil in fallow field plots during the first 101 days and the nematode was not detected after 263 days. Bioassays subsequently failed to detect the nematode in the upper 30 cm of soil in fallow plots on days 263 and 365. Population densities also decreased rapidly in fallow soil during the initial 130 days of the growth chamber study and the nematode was not detected at days 334 and 427, or in subsequent bioassays. Longidorus americanus does not survive well in the upper 15-30 cm of nursery soil in the absence of a host, and the use of fallow may be an acceptable alternative to pesticides for the management of this nematode.

Influence of Tylenchorhynchus ewingi on growth of loblolly pine seedlings, and host suitability of legumes and small grains

Tylenchorhynchus ewingi, a stunt nematode, causes severe injury to slash pine seedlings and has been recently associated with stunting and chlorosis of loblolly pine seedlings at some forest tree nurseries in southern USA. Experiments confirmed that loblolly pine is a host for T. ewingi, and that the nematode is capable of causing severe damage to root systems. Initial population densities as low as 60 nematodes (100 cm3 soil)−1 were sufficient to damage the root systems of loblolly pine seedlings. Populations of T. ewingi increased on pine from two- to 16-fold, depending on the initial population density. Evaluations of various cover crops used in southern forest tree nurseries indicated that legumes, rye and several varieties of sorghum were excellent hosts for T. ewingi. Other small grains such as ryegrass, oats and wheat were poorer hosts. A cultivar of pearl millet was a non-host for T. ewingi, and a cultivar of brown top millet appeared to be either a very poor host or a non-host. Nurseries that have seedling production losses caused by T. ewingi should consider rotating with non-host cover crops such as pearl millet or leaving fields fallow as part of their pest management programme.