Birdeye pearlwort in conifer seedling nurseries in Michigan

Identifying and controlling birdeye pearlwort (Sagina procumbens L.) weed species in conifer seedling nurseries in Michigan.

Birdeye pearlwort growing in an open field
Photo 1. Birdeye pearlwort (Sagina procumbens L.) growing in an open field along with conifer seedlings in a seedling bed in west Michigan. The sandy loam soil seems to be suitable for pearlwort growth. Photo by Debalina Saha, MSU.

During my visits to several seedling nurseries in Michigan this past fall, I came across a common weed issue the seedling growers were dealing with. It was the prevalence of the birdeye pearlwort in their container production and seedling beds. The pearlwort was spreading all over the field production (Photo 1) and the small conifer seedlings were competing with it in the beds. The grower was not familiar with the weed or how to control it without damaging the seedlings. At a container nursery, the grower was having the similar issues in controlling birdeye pearlwort (Photo 2).

Hand-weeding to remove pearlwort from seedling beds or containers is extremely difficult, laborious, time-consuming and expensive as they form a mat-like structure with shallow roots that spread easily in the presence of moisture. Most often growers and homeowners can get confused between pearlwort and mosses, as they seem to be very similar (mat-like, velvety and present in moist conditions).

It is very important to identify the target weed species correctly before taking any controlling measures. Let’s discuss the features of birdeye pearlwort and possible ways to control this weed in seedling production systems.

What is birdeye pearlwort?

Birdeye pearlwort or Sagina procumbens L. is a perennial weed that is native to Eurasia and north Africa and belongs to the pink family, Caryophyllaceae. It has become acclimatized and naturalized in temperate regions. Once it becomes established, it can be difficult to eradicate due to its persistence in the seed bank.

According to Hilty, 2006, this plant grows well on sandy ridges, in open woodlands, rocky open ground and either natural or disturbed areas where there is scant vegetation on the ground. Thus, the sandy loam soil in western Michigan where most of the conifer seedlings are produced is a perfect habitat for birdeye pearlwort (Photo 1).

As noted earlier, pearlwort is a mat-forming plant and has narrow leaves ending in a bristle-like point. The root system consists of a slender taproot that is shallow and divides very frequently into secondary roots. Pairs of opposite leaves occur at intervals along the stems. Each leaf is about 0.5 inches long and bright green, like stems. It often forms a rosette of leaves from which one or more stems develop. These stems are bright green, glabrous and tend to sprawl across other stems or the ground. The stems often terminate in either individual flowers or small cyme of flowers.

The blooming period occurs from mid- to late spring and lasts about one month for a colony of plants, according to Hilty, 2006. The petals are usually shorter and narrower than the sepals; they are often missing or poorly developed in individual flowers. They reproduce by forming dark tiny seeds that are dispersed by wind. The pearlwort seedlings are frost tolerant, hence they can survive and grow in temperate climates as in Michigan.

Birdeye pearlwort growing in containers
Photo 2. Birdeye pearlwort (Sagina procumbens L.) growing in containers along with conifer seedlings. Photo by Debalina Saha, MSU.

What are the possible ways to control birdeye pearlwort?

Pearlwort is often associated with excess water in the soil or in the container. Some of the possible ways to control it are as follows.

Non-chemical method

Maintaining good sanitation practices in the nursery as well as in the field can help in controlling the pearlwort. Excessive irrigation water in the soil can increase the problem. Check water requirement of your seedlings and apply irrigation accordingly. Using overhead sprinklers can spread the pearlwort seeds more easily; alternative irrigation system such as micro or drip irrigation practices can be applied.

The source of irrigation water is also an important factor to consider, as there are higher chances of seed dispersal if irrigating from a pond than from a well. Decontaminate your tools, equipment and other machineries to reduce the dispersal of pearlwort seeds.

Chemical method

Only few preemergent herbicides have been studied for controlling pearlwort. An experiment conducted at Oregon State University by James Altland in 2003 showed excellent control (greater than 85%) of pearlwort with the granular formulations of Snapshot, Rout and Broadstar preemergent herbicides. All these preemergent herbicides are labeled for container nursery production systems. However, it is highly recommended you check the herbicide label carefully before applying the product for the correct application timing and rate of application.

More herbicide chemicals, both preemergence as well as postemergence, need to be evaluated on this weed species. In addition to the herbicides, using organic mulch materials such as rice hull, coco shell mulch, pine bark etc. need to be studied in the field as well as in the container production system as an alternative non-chemical strategy.

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